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56 results on '"accretion, accretion disk"'

1. Investigating the coronal structure by studying time lags in the Atoll source 4U 1705-44 using AstroSat.

Author

Malu, S., Harikrishna, S., Sriram, K., and Agrawal, Vivek K.

Subjects
*CORAL reefs & islands, *ACCRETION disks, *NEUTRON stars, *STATISTICAL correlation, *SOLAR corona, *CROSS correlation
Abstract

We performed a detailed timing study of the Atoll source 4U 1705-44 in order to understand the accretion disk geometry. Cross correlation function (CCF) studies were performed between soft (3-5 keV) and hard energy (15-30 keV) bands using the AstroSat LAXPC data. We detected hard as well as soft lags of the order of few ten to hundred seconds. A dynamical CCF study was performed in the same energy bands for one of the light curves and we found smaller lags of few tens of seconds (<50 s) suggesting that the variation is probably originating from the corona. We found a broad noise component around ∼13 Hz in the 3-10 keV band which is absent in 10-20 keV band. We interpret the observed lags as the readjustment timescales of the corona or a boundary layer around the neutron star and constrain the height of this structure to few tens of km. We independently estimated the coronal height to be around 15 km assuming that the 13 Hz feature in the PDS is originating from the oscillation of the viscous shell around the neutron star. [ABSTRACT FROM AUTHOR]

Published
2021
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2. The ionizing and heating power of ultraluminous X-ray sources under the geometrical beaming model

Author

K. Kovlakas, T. Fragos, D. Schaerer, A. Mesinger, Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Kovlakas, K., Fragos, T., Schaerer, D., and Mesinger, A.

Subjects
galaxie [X-rays], High Energy Astrophysical Phenomena (astro-ph.HE), binarie [X-rays], accretion disks, FOS: Physical sciences, Astronomy and Astrophysics, accretion, accretion disk, Astrophysics - Astrophysics of Galaxies, X-rays: ISM, X-rays: binaries, X-rays: galaxies, Settore FIS/05 - Astronomia e Astrofisica, accretion, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), ultraviolet: galaxies, ISM [X-rays], galaxie [ultraviolet], [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

While there is now a consensus that X-ray binaries (XRBs) are the dominant X-ray sources in the early Universe and play a significant role during the epoch of heating of the intergalactic medium (IGM), recent studies report contradicting results regarding their contribution in the nebular emission of local Universe galaxies. Ultraluminous X-ray sources (ULXs), which dominate the X-ray budget of normal galaxies, may be important interstellar-medium (ISM) ionizing sources. However, their output in the extreme UV (EUV) and soft--X-ray part of the spectrum remains observationally unconstrained. In this paper, we predict the ionizing and heating power from ULX populations under the geometrical beaming scenario, and three models describing the emission from super-critical accretion disks. We find that our theoretical spectra for ULX populations cannot (can) explain the HeII (NeV) emission observed in some galaxies, with their contribution being less (more) important than the underlying stellar population. Stochastic fluctuations in the number of ULXs may allow for equal contributions in the HeII emission, in a fraction of galaxies. We provide average spectra of ULX populations as an input to local, and early-Universe studies. We find that the soft--X-ray emission arising from super-critical accretion is significant for the heating of the IGM, and consistent with recent constraints from the 21-cm cosmic signal. Based on the dependence on the adopted compact-object (CO) mass and accretion model, we encourage efforts in modeling ULX spectra via simulations, and their combination with detailed binary population synthesis models., 8 pages. 6 figures, 1 table. This article has been accepted for publication in the Astronomy & Astrophysics journal. The full Table 1 will be made available via CDS

Published
2022

3. Reflection component in the Bright Atoll Source GX 9+9

Author

Angelo Gambino, A. Sanna, A. Riggio, A. Marino, T. Di Salvo, R. Iaria, S. M. Mazzola, Luciano Burderi, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Iaria R., Mazzola S.M., Di Salvo T., Marino A., Gambino A.F., Sanna A., Riggio A., and Burderi L.

Subjects
Photon, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Color temperature, 010502 geochemistry & geophysics, 01 natural sciences, Spectral line, X-rays: binaries, stars: neutron, Accretion, accretion disk, Settore FIS/05 - Astronomia E Astrofisica, accretion, 0103 physical sciences, Black-body radiation, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), accretion disks, Astronomy and Astrophysics, X-rays: binarie, Accretion (astrophysics), Neutron star, Space and Planetary Science, Electron temperature, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Low Mass, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], stars: individual: GX 9+9
Abstract

GX 9+9 (4U 1728-16) is a low mass X-ray binary (LMXB) source harboring a neutron star. Although it belongs to the subclass of the bright Atoll sources together with GX 9+1, GX 3+1, and GX 13+1, its broadband spectrum is poorly studied and apparently does not show reflection features in the spectrum. To constrain the continuum well and verify whether a relativistic smeared reflection component is present, we analyze the broadband spectrum of GX 9+9 using {\it BeppoSAX} and \textit{XMM-Newton} spectra covering the 0.3-40 keV energy band. We fit the spectrum adopting a model composed of a disk-blackbody plus a Comptonized component whose seed photons have a blackbody spectrum (Eastern Model). A statistically equivalent model is composed of a Comptonized component whose seed photons have a disk-blackbody distribution plus a blackbody that mimics a saturated Comptonization likely associated with a boundary layer (Western model). Other trials did not return a good fit. The spectrum of GX 9+9 was observed in a soft state and its luminosity is $2.3 \times 10^{37}$ erg s$^{-1}$ assuming a distance to the source of 5 kpc. In the Eastern Model scenario, we find the seed-photon temperature and electron temperature of the Comptonized component to be $1.14^{+0.10}_{-0.07}$ keV and $2.80^{+0.09}_{-0.04}$ keV, respectively, while the optical depth of the Comptonizing corona is $8.9\pm0.4$. The color temperature of the inner accretion disk is $0.86^{+0.08}_{-0.02}$ keV and $0.82 \pm 0.02$ keV for the {\it BeppoSAX} and \textit{XMM-Newton} spectrum, respectively. In the Western Model scenario, instead, we find that the seed-photon temperature is $0.87 \pm 0.07$ keV and $1.01 \pm 0.08$ keV for the {\it BeppoSAX} and \textit{XMM-Newton} spectrum, respectively. (Abridged abstract), Comment: 10 pages, 8 figures, accepted by Astronomy & Astrophysics

Published
2020

5. Variation of the gas and radiation content in the sub-Keplerian accretion disk around black holes and its impact to the solutions

Author

Mukhopadhyay, Banibrata and Dutta, Parikshit

Subjects
*SUPERMASSIVE black holes, *ACCRETION disks, *COAL gas, *RADIATION chemistry, *ASTRONOMICAL observations, *ASTROPHYSICS, *POLYTROPES
Abstract

Abstract: We investigate the variation of the gas and the radiation pressure in accretion disks during the infall of matter to the black hole and its effect to the flow. While the flow far away from the black hole might be non-relativistic, in the vicinity of the black hole it is expected to be relativistic behaving more like radiation. Therefore, the ratio of gas pressure to total pressure (β) and the underlying polytropic index (γ) should not be constant throughout the flow. We obtain that accretion flows exhibit significant variation of β and then γ, which affects solutions described in the standard literature based on constant β. Certain solutions for a particular set of initial parameters with a constant β do not exist when the variation of β is incorporated appropriately. We model the viscous sub-Keplerian accretion disk with a nonzero component of advection and pressure gradient around black holes by preserving the conservations of mass, momentum, energy, supplemented by the evolution of β. By solving the set of five coupled differential equations, we obtain the thermo-hydrodynamical properties of the flow. We show that during infall, β of the flow could vary up to ∼300%, while γ up to ∼20%. This might have a significant impact to the disk solutions in explaining observed data, e.g. super-luminal jets from disks, luminosity, and then extracting fundamental properties from them. Hence any conclusion based on constant γ and β should be taken with caution and corrected. [Copyright &y& Elsevier]

Published
2012
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6. First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring

Author

Michael Janssen, Joseph Neilsen, Gopal Narayanan, Alexander W. Raymond, Gregory Desvignes, Thomas Bronzwaer, Anne Kathrin Baczko, Alan E. E. Rogers, Ru-Sen Lu, Feryal Özel, Qingwen Wu, Shan Shan Zhao, Monika Moscibrodzka, Chunchong Ni, Michael Titus, Freek Roelofs, Buell T. Jannuzi, Tod R. Lauer, Wen Ping Lo, Geoffrey C. Bower, James M. Moran, Taehyun Jung, Bart Ripperda, Dominique Broguiere, Luciano Rezzolla, Jongsoo Kim, Jirong Mao, Jonathan Weintroub, Colin J. Lonsdale, Laurent Loinard, Daniel Michalik, John Conway, Nicholas R. MacDonald, Olivier Gentaz, Iniyan Natarajan, Izumi Mizuno, Vincent L. Fish, Eduardo Ros, Minfeng Gu, Ilse van Bemmel, Kotaro Moriyama, David J. James, Michael D. Johnson, Vincent Piétu, Daryl Haggard, Richard L. Plambeck, Lynn D. Matthews, Avery E. Broderick, Ilje Cho, Katherine L. Bouman, Karl Friedrich Schuster, Ronald Hesper, Zheng Meyer-Zhao, Daniel C. M. Palumbo, Roman Gold, Koushik Chatterjee, Bong Won Sohn, Makoto Inoue, Rebecca Azulay, Paul Tiede, Alan P. Marscher, Ziri Younsi, Ye-Fei Yuan, Jason Dexter, Venkatessh Ramakrishnan, Michael Lindqvist, Michael Bremer, Carsten Kramer, Ramesh Karuppusamy, Michael Kramer, Chi-kwan Chan, R. P. Eatough, Shiro Ikeda, Jan Wagner, Oliver Porth, Garrett K. Keating, Yi Chen, Tuomas Savolainen, Neil M. Nagar, Chet Ruszczyk, Per Friberg, Michael H. Hecht, Huib Jan van Langevelde, Alan L. Roy, Kazunori Akiyama, Jordy Davelaar, Sang-Sung Lee, Maciek Wielgus, Jason SooHoo, Lei Huang, Hiroshi Nagai, Keiichi Asada, David Ball, Thomas P. Krichbaum, A. Nadolski, Roger Brissenden, Mislav Baloković, Roberto Neri, Svetlana G. Jorstad, Des Small, Shami Chatterjee, Raquel Fraga-Encinas, Michael A. Nowak, Hiroaki Nishioka, Mark G. Rawlings, S. Sánchez, Dominic W. Pesce, Heino Falcke, Roberto Garcia, Luis C. Ho, Yan-Rong Li, Fumie Tazaki, Jessica Dempsey, Sera Markoff, David H. Hughes, Daniel R. van Rossum, Elisabetta Liuzzo, Christian M. Fromm, Cornelia Müller, Yuzhu Cui, Jun Yi Koay, Mahito Sasada, Geoffrey B. Crew, Norbert Wex, Nimesh A. Patel, Ed Fomalont, Chih-Wei Locutus Huang, Lijing Shao, Christiaan D. Brinkerink, David Sánchez-Arguelles, Laura Vertatschitsch, Remo P. J. Tilanus, Andrew Chael, Shuichiro Tsuda, Dan Bintley, Ciriaco Goddi, Ramesh Narayan, Charles F. Gammie, Tyler Trent, Mel Rose, Feng Yuan, Satoki Matsushita, Robert Wharton, Jadyn Anczarski, F. Peter Schloerb, Patrick M. Koch, Kazi L.J. Rygl, Nicolas Pradel, Britton Jeter, Tomohisa Kawashima, Shuo Zhang, John E. Carlstrom, Jae-Young Kim, Junhan Kim, Arash Roshanineshat, Jorge A. Preciado-López, Benjamin R. Ryan, Sara Issaoun, Hector Olivares, Andreas Eckart, Hiroki Okino, Karl M. Menten, Lia Medeiros, Zhiqiang Shen, Mariafelicia De Laurentis, Kuo Liu, Joseph R. Farah, Aristeidis Noutsos, Mark Kettenis, C. Y. Kuo, Wu Jiang, Zhiyuan Li, Boris Georgiev, W. Boland, Ramprasad Rao, Guang-Yao Zhao, Ming-Tang Chen, Mansour Karami, José L. Gómez, André Young, Pablo Torne, John Wardle, Ben Prather, Shoko Koyama, Rurik A. Primiani, Pierre Christian, Walter Alef, Kamal Souccar, Paul T. P. Ho, Andrei P. Lobanov, George N. Wong, Kazuhiro Hada, Ziyan Zhu, Silke Britzen, J. Anton Zensus, Ue-Li Pen, Yosuke Mizuno, Sascha Trippe, Sheperd S. Doeleman, James M. Cordes, John E. Barrett, Peter Galison, Dimitrios Psaltis, Mareki Honma, Daniel P. Marrone, Masanori Nakamura, Frederick K. Baganoff, Aleksandar Popstefanija, Helge Rottmann, Mark Gurwell, Ivan Marti-Vidal, Hung Yi Pu, Tomoaki Oyama, Motoki Kino, Roger Deane, Ken H. Young, Paul Yamaguchi, Lindy Blackburn, Kenji Toma, Do-Young Byun, Antxon Alberdi, Academy of Finland, European Commission, Alexander von Humboldt Foundation, John Templeton Foundation, China Scholarship Council, Comisión Nacional de Investigación Científica y Tecnológica (Chile), Consejo Nacional de Ciencia y Tecnología (México), European Research Council, Generalitat Valenciana, Ministerio de Economía, Industria y Competitividad (España), Ministerio de Ciencia, Innovación y Universidades (España), Gordon and Betty Moore Foundation, Istituto Nazionale di Fisica Nucleare, Japan Society for the Promotion of Science, Japanese Government, Chinese Academy of Sciences, Max Planck Society, Ministry of Science and Technology (Taiwan), National Aeronautics and Space Administration (US), National Science Foundation (US), National Natural Science Foundation of China, National Research Foundation of Korea, Netherlands Organization for Scientific Research, Natural Sciences and Engineering Research Council of Canada, Russian Science Foundation, National Research Foundation (South Africa), Ministero dell'Istruzione, dell'Università e della Ricerca, Alberdi, Antxón, Gómez Fernández, J. L., Institut de RadioAstronomie Millimétrique (IRAM), Centre National de la Recherche Scientifique (CNRS), Instituto de RadioAstronomía Milimétrica (IRAM), Event Horizon Telescope, Event Horizon Telescope Collaboration, T., Akiyama, K., Alberdi, A., Alef, W., Asada, K., Azulay, R., Baczko, A. -K., Ball, D., Balokovic, M., Barrett, J., Bintley, D., Blackburn, L., Boland, W., Bouman, K. L., Bower, G. C., Bremer, M., Brinkerink, C. D., Brissenden, R., Britzen, S., Broderick, A. E., Broguiere, D., Bronzwaer, T., Byun, D. -Y., Carlstrom, J. E., Chael, A., Chan, C. -K., Chatterjee, S., Chatterjee, K., Chen, M. -T., Chen, Y., Cho, I., Christian, P., Conway, J. E., Cordes, J. M., Crew, G. B., Cui, Y., Davelaar, J., De Laurentis, M., Deane, R., Dempsey, J., Desvignes, G., Dexter, J., Doeleman, S. S., Eatough, R. P., Falcke, H., Fish, V. L., Fomalont, E., Fraga-Encinas, R., Friberg, P., Fromm, C. M., Gomez, J. L., Galison, P., Gammie, C. F., Garcia, R., Gentaz, O., Georgiev, B., Goddi, C., Gold, R., Gu, M., Gurwell, M., Hada, K., Hecht, M. H., Hesper, R., Ho, L. C., Ho, P., Honma, M., Huang, C. -W. L., Huang, L., Hughes, D. H., Ikeda, S., Inoue, M., Issaoun, S., James, D. J., Jannuzi, B. T., Janssen, M., Jeter, B., Jiang, W., Johnson, M. D., Jorstad, S., Jung, T., Karami, M., Karuppusamy, R., Kawashima, T., Keating, G. K., Kettenis, M., Kim, J. -Y., Kim, J., Kino, M., Koay, J. Y., Koch, P. M., Koyama, S., Kramer, M., Kramer, C., Krichbaum, T. P., Kuo, C. -Y., Lauer, T. R., Lee, S. -S., Li, Y. -R., Li, Z., Lindqvist, M., Liu, K., Liuzzo, E., Lo, W. -P., Lobanov, A. P., Loinard, L., Lonsdale, C., Lu, R. -S., Macdonald, N. R., Mao, J., Markoff, S., Marrone, D. P., Marscher, A. P., Marti-Vidal, I., Matsushita, S., Matthews, L. D., Medeiros, L., Menten, K. M., Mizuno, Y., Mizuno, I., Moran, J. M., Moriyama, K., Moscibrodzka, M., Muller, C., Nagai, H., Nagar, N. M., Nakamura, M., Narayan, R., Narayanan, G., Natarajan, I., Neri, R., Ni, C., Noutsos, A., Okino, H., Olivares, H., Oyama, T., Ozel, F., Palumbo, D. C. M., Patel, N., Pen, U. -L., Pesce, D. W., Pietu, V., Plambeck, R., Popstefanija, A., Porth, O., Prather, B., Preciado-Lopez, J. A., Psaltis, D., Pu, H. -Y., Ramakrishnan, V., Rao, R., Rawlings, M. G., Raymond, A. W., Rezzolla, L., Ripperda, B., Roelofs, F., Rogers, A., Ros, E., Rose, M., Roshanineshat, A., Rottmann, H., Roy, A. L., Ruszczyk, C., Ryan, B. R., Rygl, K. L. J., Sanchez, S., Sanchez-Arguelles, D., Sasada, M., Savolainen, T., Schloerb, F. P., Schuster, K. -F., Shao, L., Shen, Z., Small, D., Sohn, B. W., Soohoo, J., Tazaki, F., Tiede, P., Tilanus, R. P. J., Titus, M., Toma, K., Torne, P., Trent, T., Trippe, S., Tsuda, S., Van Bemmel, I., Van Langevelde, H. J., Van Rossum, D. R., Wagner, J., Wardle, J., Weintroub, J., Wex, N., Wharton, R., Wielgus, M., Wong, G. N., Wu, Q., Young, A., Young, K., Younsi, Z., Yuan, F., Yuan, Y. -F., Zensus, J. A., Zhao, G., Zhao, S. -S., Zhu, Z., Anczarski, J., Baganoff, F. K., Eckart, A., Farah, J. R., Haggard, D., Meyer-Zhao, Z., Michalik, D., Nadolski, A., Neilsen, J., Nishioka, H., Nowak, M. A., Pradel, N., Primiani, R. A., Souccar, K., Vertatschitsch, L., Yamaguchi, P., Zhang, S., Astronomy, High Energy Astrophys. & Astropart. Phys (API, FNWI), Gravitation and Astroparticle Physics Amsterdam, Anne Lähteenmäki Group, Department of Electronics and Nanoengineering, Aalto-yliopisto, Aalto University, Alberdi, Antxón [0000-0002-9371-1033], and Gómez Fernández, J. L. [0000-0003-4190-7613]

Subjects
Magnetohydrodynamics (MHD), 010504 meteorology & atmospheric sciences, individual (M87) [galaxies], Event horizon, galaxies: jet, Astronomy, Strong gravitational lensing, black hole physics, jets [galaxies], galaxies: individual, Astrophysics, accretion, accretion disk, 01 natural sciences, General Relativity and Quantum Cosmology, Galaxies: individual (M87), accretion, 010303 astronomy & astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, accretion, accretion disks, accretion disks, high angular resolution [techniques], Accretion disks, (MHD), Astrophysics - High Energy Astrophysical Phenomena, General relativity, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, General Relativity and Quantum Cosmology (gr-qc), Compact star, galaxies: individual: M87, magnetohydrodynamics (MHD), Techniques: high angular resolution, 0103 physical sciences, (M87), 0105 earth and related environmental sciences, Event Horizon Telescope, Supermassive black hole, Astronomy and Astrophysics, Black hole physics, Astrophysics - Astrophysics of Galaxies, black hole physic, Black hole, Rotating black hole, Space and Planetary Science, magnetohydrodynamics: MHD, Galaxies: jets, Astrophysics of Galaxies (astro-ph.GA), magnetohydrodynamics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 EHT data. To this end, we construct a large library of models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. The ring radius and ring asymmetry depend on black hole mass and spin, respectively, and both are therefore expected to be stable when observed in future EHT campaigns. Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. If the black hole spin and M87's large scale jet are aligned, then the black hole spin vector is pointed away from Earth. Models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets. At the same time, in those models that produce a sufficiently powerful jet, the latter is powered by extraction of black hole spin energy through mechanisms akin to the Blandford-Znajek process. We briefly consider alternatives to a black hole for the central compact object. Analysis of existing EHT polarization data and data taken simultaneously at other wavelengths will soon enable new tests of the GRMHD models, as will future EHT campaigns at 230 and 345 GHz.© 2019. The American Astronomical Society., The authors of this Letter thank the following organizations and programs: the Academy of Finland (projects 274477, 284495, 312496); the Advanced European Network of E-infrastructures for Astronomy with the SKA (AENEAS) project, supported by the European Commission Framework Programme Horizon 2020 Research and Innovation action under grant agreement 731016; the Alexander von Humboldt Stiftung; the Black Hole Initiative at Harvard University, through a grant (60477) from the John Templeton Foundation; the China Scholarship Council; Comisión Nacional de Investigación Científica y Tecnológica (CONICYT, Chile, via PIA ACT172033, Fondecyt 1171506, BASAL AFB170002, ALMA-conicyt 31140007); Consejo Nacional de Ciencia y Tecnología (CONACYT, Mexico, projects 104497, 275201, 279006, 281692); the Delaney Family via the Delaney Family John A. Wheeler Chair at Perimeter Institute; Dirección General de Asuntos del Personal Académico-Universidad Nacional 9 The Astrophysical Journal Letters, 875:L1 (17pp), 2019 April 10 The EHT Collaboration et al. Autónoma de México (DGAPA-UNAM, project IN112417); the European Research Council (ERC) Synergy Grant “BlackHoleCam: Imaging the Event Horizon of Black Holes” (grant 610058); the Generalitat Valenciana postdoctoral grant APOSTD/2018/177; the Gordon and Betty Moore Foundation (grants GBMF-3561, GBMF-5278); the Istituto Nazionale di Fisica Nucleare (INFN) sezione di Napoli, iniziative specifiche TEONGRAV; the International Max Planck Research School for Astronomy and Astrophysics at the Universities of Bonn and Cologne; the Jansky Fellowship program of the National Radio Astronomy Observatory (NRAO); the Japanese Government (Monbukagakusho: MEXT) Scholarship; the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for JSPS Research Fellowship (JP17J08829); JSPS Overseas Research Fellowships; the Key Research Program of Frontier Sciences, Chinese, Academy of Sciences (CAS, grants QYZDJ-SSW-SLH057, QYZDJ-SSW-SYS008); the Leverhulme Trust Early Career Research Fellowship; the Max-Planck-Gesellschaft (MPG); the Max Planck Partner Group of the MPG and the CAS; the MEXT/JSPS KAKENHI (grants 18KK0090, JP18K13594, JP18K03656, JP18H03721, 18K03709, 18H01245, 25120007); the MIT International Science and Technology Initiatives (MISTI) Funds; the Ministry of Science and Technology (MOST) of Taiwan (105-2112-M-001-025-MY3, 106-2112-M001-011, 106-2119-M-001-027, 107-2119-M-001-017, 107- 2119-M-001-020, and 107-2119-M-110-005); the National Aeronautics and Space Administration (NASA, Fermi Guest Investigator grant 80NSSC17K0649); the National Institute of Natural Sciences (NINS) of Japan; the National Key Research and Development Program of China (grant 2016YFA0400704, 2016YFA0400702); the National Science Foundation (NSF, grants AST-0096454, AST-0352953, AST-0521233, AST0705062, AST-0905844, AST-0922984, AST-1126433, AST1140030, DGE-1144085, AST-1207704, AST-1207730, AST1207752, MRI-1228509, OPP-1248097, AST-1310896, AST1312651, AST-1337663, AST-1440254, AST-1555365, AST1715061, AST-1615796, AST-1614868, AST-1716327, OISE1743747, AST-1816420); the Natural Science Foundation of China (grants 11573051, 11633006, 11650110427, 10625314, 11721303, 11725312, 11873028, 11873073, U1531245, 11473010); the Natural Sciences and Engineering Research Council of Canada (NSERC, including a Discovery Grant and the NSERC Alexander Graham Bell Canada Graduate Scholarships-Doctoral Program); the National Youth Thousand Talents Program of China; the National Research Foundation of Korea (grant 2015-R1D1A1A01056807, the Global PhD Fellowship Grant: NRF-2015H1A2A1033752, and the Korea Research Fellowship Program: NRF-2015H1D3A1066561); the Netherlands Organization for Scientific Research (NWO) VICI award (grant 639.043.513) and Spinoza Prize (SPI 78-409); the New Scientific Frontiers with Precision, Radio Interferometry Fellowship awarded by the South African Radio Astronomy Observatory (SARAO), which is a facility of the National Research Foundation (NRF), an agency of the Department of Science and Technology (DST) of South Africa; the Onsala Space Observatory (OSO) national infrastructure, for the provisioning of its facilities/observational support (OSO receives funding through the Swedish Research Council under grant 2017-00648); the Perimeter Institute for Theoretical Physics (research at Perimeter Institute is supported by the Government of Canada through the Department of Innovation, Science and Economic Development Canada and by the Province of Ontario through the Ministry of Economic Development, Job Creation and Trade); the Russian Science Foundation (grant 17-12-01029); the Spanish Ministerio de Economía y Competitividad (grants AYA2015-63939-C2-1-P, AYA2016-80889-P); the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709); the Toray Science Foundation; the US Department of Energy (USDOE) through the Los Alamos National Laboratory (operated by Triad National Security, LLC, for the National Nuclear Security Administration of the USDOE (Contract 89233218CNA000001)); the Italian Ministero dell’Istruzione Università e Ricerca through the grant Progetti Premiali 2012-iALMA (CUP C52I13000140001); the European Unionʼs Horizon 2020 research and innovation programme under grant agreement No 730562 RadioNet; ALMA North America Development Fund; Chandra TM6-17006X

Published
2019

7. Prolonged sub-luminous state of the new transitional pulsar candidate CXOU J110926.4-650224

Author

Carlo Ferrigno, D. de Martino, Alida Odendaal, Alessandro Papitto, Thomas D. Russell, Francesco Coti Zelati, Sergio Campana, David A. H. Buckley, S. M. Mazzola, Mariusz Gromadzki, Jian Li, Diego F. Torres, Simone Migliari, Nanda Rea, Enrico Bozzo, High Energy Astrophys. & Astropart. Phys (API, FNWI), Coti Zelati F., Papitto A., De Martino D., Buckley D.A.H., Odendaal A., Li J., Russell T.D., Torres D.F., Mazzola S.M., Bozzo E., Gromadzki M., Campana S., Rea N., Ferrigno C., Migliari S., DEU, and ESP

Subjects
Photon, X-rays: Binarie, Astrophysics::High Energy Astrophysical Phenomena, Flux, FOS: Physical sciences, Astrophysics, Methods: Data analysi, Astrophysics::Cosmology and Extragalactic Astrophysics, 7. Clean energy, 01 natural sciences, Luminosity, Accretion, accretion disk, Settore FIS/05 - Astronomia E Astrofisica, Pulsar, Methods: Observational, 0103 physical sciences, Emission spectrum, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Astronomy and Astrophysics, Stars: neutron, X-rays: Individuals: CXOU J110926.4-650224, Neutron star, 13. Climate action, Space and Planetary Science, Magnitude (astronomy), Astrophysics - High Energy Astrophysical Phenomena, Fermi Gamma-ray Space Telescope
Abstract

We report on a multi-wavelength study of the unclassified X-ray source CXOU J110926.4-650224 (J1109). We identified the optical counterpart as a blue star with a magnitude of $\sim$20.1 (3300-10500 $\require{mediawiki-texvc} \AA$). The optical emission was variable on timescales from hundreds to thousands of seconds. The spectrum showed prominent emission lines with variable profiles at different epochs. Simultaneous XMM-Newton and NuSTAR observations revealed a bimodal distribution of the X-ray count rates on timescales as short as tens of seconds, as well as sporadic flaring activity. The average broad-band (0.3-79 keV) spectrum was adequately described by an absorbed power law model with photon index of $\Gamma$=1.63$\pm$0.01 (at 1$\sigma$ c.l.), and the X-ray luminosity was (2.16$\pm$0.04)$\times$10$^{34}$ erg s$^{-1}$ for a distance of 4 kpc. Based on observations with different instruments, the X-ray luminosity has remained relatively steady over the past $\sim$15 years. J1109 is spatially associated with the gamma-ray source FL8Y J1109.8-6500, which was detected with Fermi at an average luminosity of (1.5$\pm$0.2)$\times$10$^{34}$ erg s$^{-1}$ (assuming the distance of J1109) over the 0.1-300 GeV energy band between 2008 and 2016. The source was undetected during ATCA radio observations that were simultaneous with NuSTAR, down to a 3$\sigma$ flux upper limit of 18 $\mu$Jy/beam (at 7.25 GHz). We show that the phenomenological properties of J1109 point to a binary transitional pulsar candidate currently in a sub-luminous accretion disk state, and that the upper limits derived for the radio emission are consistent with the expected radio luminosity for accreting neutron stars at similar X-ray luminosities., Comment: 21 pages, 15 figures, accepted for publication in A&A

Published
2019
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8. NuSTAR Measurement of Coronal Temperature in Two Luminous, High-redshift Quasars

Author

Francesco Tombesi, Enrico Piconcelli, Roberto Gilli, Massimo Cappi, Francesca Civano, W. N. Brandt, George Chartas, C. Vignali, Giorgio Lanzuisi, Marcella Brusa, Andrea Comastri, Stefano Bianchi, Massimo Gaspari, Mauro Dadina, R. Middei, Andrea Marinucci, Lanzuisi, G., Gilli, R., Cappi, M., Dadina, M., Bianchi, S., Brusa, M., Chartas, G., Civano, F., Comastri, A., Marinucci, A., Middei, R., Piconcelli, E., Vignali, C., Brandt, W. N., Tombesi, F., Gaspari, M., Lanzuisi G., Gilli R., Cappi M., Dadina M., Bianchi S., Brusa M., Chartas G., Civano F., Comastri A., Marinucci A., Middei R., Piconcelli E., Vignali C., Brandt W. N., Tombesi F., Gaspari M., ITA, and USA

Subjects
Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, accretion, accretion disks, black hole physics, X-rays: galaxies, Astrophysics - High Energy Astrophysical Phenomena, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, accretion, accretion disk, black hole physic, Accretion (astrophysics), Redshift, galaxies [X-rays], Accretion disc, Settore FIS/05 - Astronomia e Astrofisica, Space and Planetary Science, Astrophysics::Solar and Stellar Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract

X-ray emission from AGN is believed to be produced via Comptonization of optical/UV seed photons emitted by the accretion disk, up-scattered by hot electrons in a corona surrounding the black hole. A critical compactness vs. temperature threshold is predicted above which any increase in the source luminosity, for a fixed size, would then generate positron-electron pairs rather than continue heating the coronal plasma. Current observations seem to confirm that all AGN populate the region below this critical line. These models, however, have never been probed by observations in the high-luminosity regime, where the critical line is expected to reach low temperatures. To fill this observational gap, we selected two luminous ($log(L_{bol})>47.5$ erg/s) quasars, 2MASSJ1614346+470420 ($z=1.86$) and B1422+231 ($z=3.62$), and obtained XMM-Newton and NuSTAR deep observations for them. We performed detailed spectral analysis of their quasi-simultaneous soft and hard X-ray data, in order to constrain the parameters of their coronae. Using a phenomenological cut-off power-law model, with the inclusion of a reflection component, we derived rest-frame values of the high energy cut-off of $E_{cut}=106^{+102}_{-37}$ keV and $E_{cut}=66^{+17}_{-12}$ keV, respectively. Comptonization models consistently give as best-fit parameters electron temperatures of $\sim45$ keV and $\sim28$ keV, respectively, and optically thick coronae ($��>1$). These low coronal temperatures fall in the limited region allowed at these luminosities to avoid runaway pair production., 8 pages, 2 figures, accepted for publication in ApJ Letter

Published
2019

9. New view of the corona of classical T Tauri stars: Effects of flaring activity in circumstellar disks

Author

Fabio Reale, Rosaria Bonito, Giovanni Peres, Costanza Argiroffi, S. Colombo, L. Ibgui, C. Stehlé, Salvatore Orlando, ITA, FRA, Università degli studi di Palermo - University of Palermo, Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA (UMR_8112)), Sorbonne Université (SU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Cergy Pontoise (UCP), Université Paris-Seine-Université Paris-Seine-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), INAF - Osservatorio Astronomico di Palermo (OAPa), Istituto Nazionale di Astrofisica (INAF), Politecnico di Milano [Milan] (POLIMI), Colombo, S., Orlando, S., Peres, G., Reale, F., Argiroffi, C., Bonito, R., Ibgui, L., and Stehlé, C.

Subjects
Young stellar object, Stars: flare, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, X-rays: stars, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, accretion, accretion disk, 01 natural sciences, magnetohydrodynamics (MHD), Settore FIS/05 - Astronomia E Astrofisica, accretion, 0103 physical sciences, Radiative transfer, Protostar, Astrophysics::Solar and Stellar Astrophysics, Stars: coronae, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, Physics, 010308 nuclear & particles physics, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], accretion disks, Stellar magnetic field, Astronomy and Astrophysics, [PHYS.ASTR.SR]Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Corona, Accretion (astrophysics), T Tauri star, Astrophysics - Solar and Stellar Astrophysics, Heat flux, 13. Climate action, Space and Planetary Science, Stars: pre-main sequence, Astrophysics::Earth and Planetary Astrophysics
Abstract

Classical T Tauri stars (CTTSs) are young low-mass stellar objects accreting mass from their circumstellar disks. They are characterized by high levels of coronal activity as revealed by X-ray observations. This activity may affect the disk stability and the circumstellar environment. Here we investigate if an intense coronal activity due to flares occurring close to the accretion disk may perturb the inner disk stability, disrupt the inner part of the disk and, possibly, trigger accretion phenomena with rates comparable with those observed. We model a magnetized protostar surrounded by an accretion disk through 3D magnetohydrodinamic simulations. We explore cases characterized by a dipole plus an octupole stellar magnetic field configuration and different density of the disk or by different levels of flaring activity. As a result of the simulated intense flaring activity, we observe the formation of several loops that link the star to the disk; all these loops build up a hot extended corona with an X-ray luminosity comparable with typical values observed in CTTSs. The intense flaring activity close to the disk can strongly perturb the disk stability. The flares trigger overpressure waves which travel through the disk and modify its configuration. Accretion funnels may be triggered by the flaring activity, thus contributing to the mass accretion rate of the star. Accretion rates synthesized from the simulations are in a range between 10^-10 and 10^-9M_sun yr^-1 The accretion columns can be perturbed by the flares and they can interact with each other, possibly merging together in larger streams. As a result, the accretion pattern can be rather complex: the streams are highly inhomogeneous, with a complex density structure, and clumped, Comment: 12 pages, 9 figures

Published
2019

10. Discovery of 105 Hz coherent pulsations in the ultracompact binary IGR J16597-3704

Author

Craig O. Heinke, Andrea Possenti, M. Burgay, Enrico Bozzo, Nathalie Degenaar, Thomas J. Maccarone, Gregory R. Sivakoff, T. Di Salvo, R. Iaria, A. Sanna, Rudy Wijnands, A. Riggio, Luciano Burderi, Diego Altamirano, Carlo Ferrigno, Arash Bahramian, Alessandro Papitto, N. D'Amico, Sanna, A., Bahramian, A., Bozzo, E., Heinke, C., Altamirano, D., Wijnands, R., Degenaar, N., Maccarone, T., Riggio, A., Di Salvo, T., Iaria, R., Burgay, M., Possenti, A., Ferrigno, C., Papitto, A., Sivakoff, G.R., D'Amico, N., Burderi, L., and High Energy Astrophys. & Astropart. Phys (API, FNWI)

Subjects
Photon, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, symbols.namesake, Accretion, accretion disk, Settore FIS/05 - Astronomia E Astrofisica, 0103 physical sciences, Binaries: general, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Accretion (meteorology), 010308 nuclear & particles physics, general, Stars: neutron, X-rays: binaries, Astronomy and Astrophysics, Space and Planetary Science [Accretion, accretion disks, Binaries], Astronomy and Astrophysic, Light curve, Orbital period, X-rays: binarie, Neutron star, Space and Planetary Science, Globular cluster, symbols, Electron temperature, Astrophysics - High Energy Astrophysical Phenomena, Doppler effect
Abstract

We report the discovery of X-ray pulsations at 105.2 Hz (9.5 ms) from the transient X-ray binary IGR J16597-3704 using NuSTAR and Swift. The source was discovered by INTEGRAL in the globular cluster NGC 6256 at a distance of 9.1 kpc. The X-ray pulsations show a clear Doppler modulation implying an orbital period of ~46 minutes and a projected semi-major axis of ~5 lt-ms, which makes IGR J16597-3704 an ultra-compact X-ray binary system. We estimated a minimum companion mass of 0.0065 solar masses, assuming a neutron star mass of 1.4 solar masses, and an inclination angle of, 4 pages, 4 images, Accepted for publication in A&A

Published
2018

11. The Spectral and Environment Properties of z ∼ 2.0-2.5 Quasar Pairs

Author

Joseph F. Hennawi, Jason X. Prochaska, John M. O'Meara, Tom Theuns, Marcel Neeleman, Michele Fumagalli, Marc Rafelski, Elisabeta Lusso, Lusso, E, Fumagalli, M, Rafelski, M, Neeleman, M, Prochaska, J, Hennawi, J, O'Meara, J, and Theuns, T

Subjects
Dark matter, galaxies: active, FOS: Physical sciences, quasars: absorption line, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, accretion, accretion disk, 01 natural sciences, quasars: general, 0103 physical sciences, Lyman continuum photons, Absorption (logic), Emission spectrum, 10. No inequality, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, 010308 nuclear & particles physics, Astronomy and Astrophysics, Quasar, Astrophysics - Astrophysics of Galaxies, Redshift, Lyman limit, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), intergalactic medium, Wide Field Camera 3
Abstract

We present the first results from our survey of intervening and proximate Lyman limit systems (LLSs) at $z$$\sim$2.0-2.5 using the Wide Field Camera 3 on-board the Hubble Space Telescope. The quasars in our sample are projected pairs with proper transverse separations $R_\perp$$\leq$150 kpc and line of sight velocity separations $\lesssim$11,000 km/s. We construct a stacked ultraviolet (rest-frame wavelengths 700-2000\AA) spectrum of pairs corrected for the intervening Lyman forest and Lyman continuum absorption. The observed spectral composite presents a moderate flux excess for the most prominent broad emission lines, a $\sim$30% decrease in flux at $\lambda$=800-900\AA\ compared to a stack of brighter quasars not in pairs at similar redshifts, and lower values of the mean free path of the HI ionizing radiation for pairs ($\lambda_{\rm mfp}^{912}=140.7\pm20.2~h_{70}^{-1}$Mpc) compared to single quasars ($\lambda_{\rm mfp}^{912}=213.8\pm28~h_{70}^{-1}$Mpc) at the average redshift $z\simeq2.44$. From the modelling of LLS absorption in these pairs, we find a higher ($\sim$20%) incidence of proximate LLSs with $\log N_{\rm HI}\geq17.2$ at $\delta v$$, Comment: Revised version with minor changes to the text following proof. Some of the references have been amended

Published
2018

12. Active Galactic Nuclei Feedback in an Elliptical Galaxy with the Most Updated AGN Physics (II): High-Angular Momentum Case

Author

Luca Ciotti, Feng Yuan, Ya-Ping Li, Doosoo Yoon, Jeremiah P. Ostriker, Zhao-Ming Gan, Yoon, Doosoo, Yuan, Feng, Gan, Zhao-Ming, Ostriker, Jeremiah P., Li, Ya-Ping, and Ciotti, Luca

Subjects
Angular momentum, Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, galaxies: active, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, accretion, accretion disk, 01 natural sciences, Specific relative angular momentum, 0103 physical sciences, Surface brightness, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Star formation, Astronomy and Astrophysics, Astronomy and Astrophysic, black hole physic, Astrophysics - Astrophysics of Galaxies, Galaxy, Black hole, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), galaxies: elliptical and lenticular, cD, Elliptical galaxy, galaxies: nuclei, galaxies: evolution, Astrophysics - High Energy Astrophysical Phenomena
Abstract

This is the second paper of our series of works of studying the effects of active galactic nuclei (AGN) feedback on the cosmological evolution of an isolated elliptical galaxy by performing two-dimensional high-resolution hydrodynamical numerical simulations. In these simulations, the inner boundary is chosen so that the Bondi radius is resolved. Physical processes like star formation, SNe Ia and II are taken into account. Compared to previous works, the main improvements is that we adopt the most updated AGN physics, which is described in detail in the first paper of this series (Yuan et al. 2018, Paper I). These improvements include the discrimination of the two accretion modes of the central AGN and the most updated descriptions of the wind and radiation in the two modes. In Paper I, we consider the case that the specific angular momentum of the gas in the galaxy is very low. In this paper, we consider the case that the specific angular momentum of the gas is high. In the galactic scale, we adopt the gravitational torques raised due to non-axisymmetric structure in the galaxy as the mechanism of the transfer of angular momentum of gas, as proposed in some recent works. Since our simulations are axisymmetric, we make use of a parameterized prescription to mimic this mechanism. Same as Paper I, we investigate the AGN light curve, typical AGN lifetime, growth of the black hole mass, AGN duty-cycle, star formation, and the X-ray surface brightness of the galaxy. Special attention is paid to the effects of specific angular momentum of the galaxy on these properties. We find that some results are qualitatively similar to those shown in Paper I, while some results such as star formation and black hole growth do show a significant difference due to the mass concentration in the galactic disk as a consequence of galactic rotation., Comment: 20 pages, 14 figures, accepted for publication to ApJ (Revised to match version published in ApJ)

Published
2018
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13. Mass Accretion Processes in Young Stellar Objects: Role of Intense Flaring Activity

Author

Andrea Mignone, Fabio Reale, Salvatore Orlando, Giovanni Peres, Orlando, S., Reale, F., Peres, G., and Mignone, A.

Subjects
Angular momentum, MHD, Stars: flare, Astrophysics::High Energy Astrophysical Phenomena, Young stellar object, FOS: Physical sciences, Interplanetary medium, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Acoustics and Ultrasonic, Accretion, accretion disk, Intermediate polar, Astrophysics::Solar and Stellar Astrophysics, X-rays: star, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, Nuclear and High Energy Physic, General Environmental Science, Physics, Radiation, Star formation, Astronomy, Accretion (astrophysics), Stars, Astrophysics - Solar and Stellar Astrophysics, lcsh:TA1-2040, Space and Planetary Science, Stars: circumstellar matter, General Earth and Planetary Sciences, Circumstellar dust, Astrophysics::Earth and Planetary Astrophysics, lcsh:Engineering (General). Civil engineering (General), Stars: pre-main-sequence
Abstract

According to the magnetospheric accretion scenario, young low-mass stars are surrounded by circumstellar disks which they interact with through accretion of mass. The accretion builds up the star to its final mass and is also believed to power the mass outflows, which may in turn have a significant role in removing the excess angular momentum from the star-disk system. Although the process of mass accretion is a critical aspect of star formation, some of its mechanisms are still to be fully understood. On the other hand, strong flaring activity is a common feature of young stellar objects (YSOs). In the Sun, such events give rise to perturbations of the interplanetary medium. Similar but more energetic phenomena occur in YSOs and may influence the circumstellar environment. In fact, a recent study has shown that an intense flaring activity close to the disk may strongly perturb the stability of circumstellar disks, thus inducing mass accretion episodes (Orlando et al. 2011). Here we review the main results obtained in the field and the future perspectives., 4 pages, 2 Figures; accepted for publication on Acta Polytechnica (Proceedings of the Frascati Workshop 2013)

Published
2014

15. Upper Limits on Gravitational Waves from Scorpius X-1 from a Model-Based Cross-Correlation Search in Advanced LIGO Data

Author

Ligo, The Scientific Collaboration, the Virgo Collaboration, Abbott, B. P., Abbott, R., Abbott, T. D., Acernese, F., Ackley, K., Adams, C., Adams, T., Addesso, P., Adhikari, R. X., Adya, V. B., Affeldt, C., Afrough, M., Agarwal, B., Agathos, M., Agatsuma, K., Aggarwal, N., Aguiar, O. D., Aiello, L., Ain, A., Ajith, P., Allen, B., Allen, G., Allocca, A., Altin, P. A., Amato, A., Ananyeva, A., Anderson, S. B., Anderson, W. G., Antier, S., Appert, S., Arai, K., Araya, M. C., Areeda, J. S., Arnaud, N., Arun, K. G., Ascenzi, S., Ashton, G., Ast, M., Aston, S. M., Astone, P., Aufmuth, P., Aulbert, C., Aultoneal, K., Avila-Alvarez, A., Babak, S., Bacon, P., Bader, M. K. M., Bae, S., Baker, P. T., Baldaccini, F., Ballardin, G., Ballmer, S. W., Banagiri, S., Barayoga, J. C., Barclay, S. E., Barish, B. C., Barker, D., Barone, F., Barr, B., Barsotti, L., Barsuglia, M., Barta, D., Bartlett, J., Bartos, I., Bassiri, R., Basti, A., Batch, J. C., Baune, C., Bawaj, M., Bazzan, M., B Ecsy, B., Beer, C., Bejger, M., Belahcene, I., Bell, A. S., Berger, B. K., Bergmann, G., Berry, C. P. L., Bersanetti, D., Bertolini, A., Betzwieser, J., Bhagwat, S., Bhandare, R., Bilenko, I. A., Billingsley, G., Billman, C. R., Birch, J., Birney, R., Birnholtz, O., Biscans, S., Bisht, A., Bitossi, M., Biwer, C., Bizouard, M. A., Blackburn, J. K., Blackman, J., Blair, C. D., Blair, D. G., Blair, R. M., Bloemen, S., Bock, O., Bode, N., Boer, M., Bogaert, G., Bohe, A., Bondu, F., Bonnand, R., Boom, B. A., Bork, R., Boschi, V., Bose, S., Bouffanais, Y., Bozzi, A., Bradaschia, C., Brady, P. R., Braginsky, V. B., Branchesi, M., Brau, J. E., Briant, T., Brillet, A., Brinkmann, M., Brisson, V., Brockill, P., Broida, J. E., Brooks, A. F., Brown, D. A., Brown, D. D., Brown, N. M., Brunett, S., Buchanan, C. C., Buikema, A., Bulik, T., Bulten, H. J., Buonanno, A., Buskulic, D., Buy, C., Byer, R. L., Cabero, M., Cadonati, L., Cagnoli, G., Cahillane, C., Calder On Bustillo, J., Callister, T. A., Calloni, E., Camp, J. B., Canepa, M., Priscilla Canizares, Cannon, K. C., Cao, H., Cao, J., Capano, C. D., Capocasa, E., Carbognani, F., Caride, S., Carney, M. F., Casanueva Diaz, J., Casentini, C., Caudill, S., Cavagli A, M., Cavalier, F., Cavalieri, R., Cella, G., Cepeda, C. B., Cerboni Baiardi, L., Cerretani, G., Cesarini, E., Chamberlin, S. J., Chan, M., Chao, S., Charlton, P., Chassande-Mottin, E., Chatterjee, D., Chatziioannou, K., Cheeseboro, B. D., Chen, H. Y., Chen, Y., Cheng, H. -P, Chincarini, A., Chiummo, A., Chmiel, T., Cho, H. S., Cho, M., Chow, J. H., Christensen, N., Chu, Q., Chua, A. J. K., Chua, S., Chung, A. K. W., Chung, S., Ciani, G., Ciolfi, R., Cirelli, C. E., Cirone, A., Clara, F., Clark, J. A., Cleva, F., Cocchieri, C., Coccia, E., Cohadon, P. -F, Colla, A., Collette, C. G., Cominsky, L. R., Constancio, M., Conti, L., Cooper, S. J., Corban, P., Corbitt, T. R., Corley, K. R., Cornish, N., Corsi, A., Cortese, S., Costa, C. A., Coughlin, M. W., Coughlin, S. B., Coulon, J. -P, Countryman, S. T., Couvares, P., Covas, P. B., Cowan, E. E., Coward, D. M., Cowart, M. J., Coyne, D. C., Coyne, R., Creighton, J. D. E., Creighton, T. D., Cripe, J., Crowder, S. G., Cullen, T. J., Cumming, A., Cunningham, L., Cuoco, E., Dal Canton, T., Danilishin, S. L., D Antonio, S., Danzmann, K., Dasgupta, A., Da Silva Costa, C. F., Dattilo, V., Dave, I., Davier, M., Davis, D., Daw, E. J., Day, B., De, S., Debra, D., Deelman, E., Degallaix, J., Laurentis, M., Del Eglise, S., Del Pozzo, W., Denker, T., Dent, T., Dergachev, V., Rosa, R., Derosa, R. T., Desalvo, R., Devenson, J., Devine, R. C., Dhurandhar, S., D Iaz, M. C., Di Fiore, L., Di Giovanni, M., Di Girolamo, T., Di Lieto, A., Di Pace, S., Di Palma, I., Di Renzo, F., Doctor, Z., Dolique, V., Donovan, F., Dooley, K. L., Doravari, S., Dorrington, I., Douglas, R., Dovale Alvarez, M., Downes, T. P., Drago, M., Drever, R. W. P., Driggers, J. C., Du, Z., Ducrot, M., Duncan, J., Dwyer, S. E., Edo, T. B., Edwards, M. C., Effler, A., Eggenstein, H. -B, Ehrens, P., Eichholz, J., Eikenberry, S. S., Eisenstein, R. A., Essick, R. C., Etienne, Z. B., Etzel, T., Evans, M., Evans, T. M., Factourovich, M., Fafone, V., Fair, H., Fairhurst, S., Fan, X., Farinon, S., Farr, B., Farr, W. M., Fauchon-Jones, E. J., Favata, M., Fays, M., Fehrmann, H., Feicht, J., Fejer, M. M., Fernandez-Galiana, A., Ferrante, I., Ferreira, E. C., Ferrini, F., Fidecaro, F., Fiori, I., Fiorucci, D., Fisher, R. P., Flaminio, R., Fletcher, M., Fong, H., Forsyth, P. W. F., Forsyth, S. S., Fournier, J. -D, Frasca, S., Frasconi, F., Frei, Z., Freise, A., Frey, R., Frey, V., Fries, E. M., Fritschel, P., Frolov, V. V., Fulda, P., Fyffe, M., Gabbard, H., Gabel, M., Gadre, B. U., Gaebel, S. M., Gair, J. R., Galloway, D. K., Gammaitoni, L., Ganija, M. R., Gaonkar, S. G., Garufi, F., Gaudio, S., Gaur, G., Gayathri, V., Gehrels, N., Gemme, G., Genin, E., Gennai, A., George, D., George, J., Gergely, L., Germain, V., Ghonge, S., Ghosh, Abhirup, Ghosh, Archisman, Ghosh, S., Giaime, J. A., Giardina, K. D., Giazotto, A., Gill, K., Glover, L., Goetz, E., Goetz, R., Gomes, S., Gonz Alez, G., Gonzalez Castro, J. M., Gopakumar, A., Gorodetsky, M. L., Gossan, S. E., Gosselin, M., Gouaty, R., Grado, A., Graef, C., Granata, M., Grant, A., Gras, S., Gray, C., Greco, G., Green, A. C., Groot, P., Grote, H., Grunewald, S., Gruning, P., Guidi, G. M., Guo, X., Gupta, A., Gupta, M. K., Gushwa, K. E., Gustafson, E. K., Gustafson, R., Hall, B. R., Hall, E. D., Hammond, G., Haney, M., Hanke, M. M., Hanks, J., Hanna, C., Hannuksela, O. A., Hanson, J., Hardwick, T., Harms, J., Harry, G. M., Harry, I. W., Hart, M. J., Haster, C. -J, Haughian, K., Healy, J., Heidmann, A., Heintze, M. C., Heitmann, H., Hello, P., Hemming, G., Hendry, M., Heng, I. 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M., Magana Hernandez, I., Magana-Sandoval, F., Magana Zertuche, L., Magee, R. M., Majorana, E., Maksimovic, I., Man, N., Mandic, V., Mangano, V., Mansell, G. L., Manske, M., Mantovani, M., Marchesoni, F., Marion, F., M Arka, S., M Arka, Z., Markakis, C., Markosyan, A. S., Maros, E., Martelli, F., Martellini, L., Martin, I. W., Martynov, D. V., Mason, K., Masserot, A., Massinger, T. J., Masso-Reid, M., Mastrogiovanni, S., Matas, A., Matichard, F., Matone, L., Mavalvala, N., Mayani, R., Mazumder, N., Mccarthy, R., Mcclelland, D. E., Mccormick, S., Mcculler, L., Mcguire, S. C., Mcintyre, G., Mciver, J., Mcmanus, D. J., Mcrae, T., Mcwilliams, S. T., Meacher, D., Meadors, G. D., Meidam, J., Mejuto-Villa, E., Melatos, A., Mendell, G., Mercer, R. A., Merilh, E. L., Merzougui, M., Meshkov, S., Messenger, C., Messick, C., Metzdorff, R., Meyers, P. M., Mezzani, F., Miao, H., Michel, C., Middleton, H., Mikhailov, E. E., Milano, L., Miller, A. L., Miller, A., Miller, B. 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B., Cowan, E. E., Coward, D. M., Cowart, M. J., Coyne, D. C., Coyne, R., Creighton, J. D. E., Creighton, T. D., Cripe, J., Crowder, S. G., Cullen, T. J., Cumming, A., Cunningham, L., Cuoco, E., Canton, T. Dal, Danilishin, S. L., D'Antonio, S., Danzmann, K., Dasgupta, A., Da Silva Costa, C. F., Dattilo, V., Dave, I., Davier, M., Davis, D., Daw, E. J., Day, B., De, S., Debra, D., Deelman, E., Degallaix, J., Laurentis, M. De, Deléglise, S., Pozzo, W. Del, Denker, T., Dent, T., Dergachev, V., De Rosa, Rosario., Derosa, R. T., Desalvo, R., Devenson, J., Devine, R. C., Dhurandhar, S., Díaz, M. C., Fiore, L. Di, Giovanni, M. Di, Di Girolamo, T., Lieto, A. Di, Pace, S. Di, Palma, I. Di, Renzo, F. Di, Doctor, Z., Dolique, V., Donovan, F., Dooley, K. L., Doravari, S., Dorrington, I., Douglas, R., Álvarez, M. Dovale, Downes, T. P., Drago, M., Drever, R. W. P., Driggers, J. C., Du, Z., Ducrot, M., Duncan, J., Dwyer, S. E., Edo, T. B., Edwards, M. C., Effler, A., Eggenstein, H. -B., Ehrens, P., Eichholz, J., Eikenberry, S. S., Eisenstein, R. A., Essick, R. C., Etienne, Z. B., Etzel, T., Evans, M., Evans, T. M., Factourovich, M., Fafone, V., Fair, H., Fairhurst, S., Fan, X., Farinon, S., Farr, B., Farr, W. M., Fauchon-Jones, E. J., Favata, M., Fays, M., Fehrmann, H., Feicht, J., Fejer, M. M., Fernandez-Galiana, A., Ferrante, I., Ferreira, E. C., Ferrini, F., Fidecaro, F., Fiori, I., Fiorucci, D., Fisher, R. P., Flaminio, R., Fletcher, M., Fong, H., Forsyth, P. W. F., Forsyth, S. S., Fournier, J. -D., Frasca, S., Frasconi, F., Frei, Z., Freise, A., Frey, R., Frey, V., Fries, E. M., Fritschel, P., Frolov, V. V., Fulda, P., Fyffe, M., Gabbard, H., Gabel, M., Gadre, B. U., Gaebel, S. M., Gair, J. R., Galloway, D. K., Gammaitoni, L., Ganija, M. R., Gaonkar, S. G., Garufi, F., Gaudio, S., Gaur, G., Gayathri, V., Gehrels, N., Gemme, G., Genin, E., Gennai, A., George, D., George, J., Gergely, L., Germain, V., Ghonge, S., Ghosh, Abhirup, Ghosh, Archisman, Ghosh, S., Giaime, J. A., Giardina, K. D., Giazotto, A., Gill, K., Glover, L., Goetz, E., Goetz, R., Gomes, S., González, G., Castro, J. M. Gonzalez, Gopakumar, A., Gorodetsky, M. L., Gossan, S. E., Gosselin, M., Gouaty, R., Grado, A., Graef, C., Granata, M., Grant, A., Gras, S., Gray, C., Greco, G., Green, A. C., Groot, P., Grote, H., Grunewald, S., Gruning, P., Guidi, G. M., Guo, X., Gupta, A., Gupta, M. K., Gushwa, K. E., Gustafson, E. K., Gustafson, R., Hall, B. R., Hall, E. D., Hammond, G., Haney, M., Hanke, M. M., Hanks, J., Hanna, C., Hannuksela, O. A., Hanson, J., Hardwick, T., Harms, J., Harry, G. M., Harry, I. W., Hart, M. J., Haster, C. -J., Haughian, K., Healy, J., Heidmann, A., Heintze, M. C., Heitmann, H., Hello, P., Hemming, G., Hendry, M., Heng, I. S., Hennig, J., Henry, J., Heptonstall, A. W., Heurs, M., Hild, S., Hoak, D., Hofman, D., Holt, K., Holz, D. E., Hopkins, P., Horst, C., Hough, J., Houston, E. A., Howell, E. J., Hu, Y. M., Huerta, E. A., Huet, D., Hughey, B., Husa, S., Huttner, S. H., Huynh-Dinh, T., Indik, N., Ingram, D. R., Inta, R., Intini, G., Isa, H. N., Isac, J. -M., Isi, M., Iyer, B. R., Izumi, K., Jacqmin, T., Jani, K., Jaranowski, P., Jawahar, S., Jiménez-Forteza, F., Johnson, W. W., Jones, D. I., Jones, R., Jonker, R. J. G., Ju, L., Junker, J., Kalaghatgi, C. V., Kalogera, V., Kandhasamy, S., Kang, G., Kanner, J. B., Karki, S., Karvinen, K. S., Kasprzack, M., Katolik, M., Katsavounidis, E., Katzman, W., Kaufer, S., Kawabe, K., Kéfélian, F., Keitel, D., Kemball, A. J., Kennedy, R., Kent, C., Key, J. S., Khalili, F. Y., Khan, I., Khan, S., Khan, Z., Khazanov, E. A., Kijbunchoo, N., Kim, Chunglee, Kim, J. C., Kim, W., Kim, W. S., Kim, Y. -M., Kimbrell, S. J., King, E. J., King, P. J., Kirchhoff, R., Kissel, J. S., Kleybolte, L., Klimenko, S., Koch, P., Koehlenbeck, S. M., Koley, S., Kondrashov, V., Kontos, A., Korobko, M., Korth, W. Z., Kowalska, I., Kozak, D. B., Krämer, C., Kringel, V., Krishnan, B., Królak, A., Kuehn, G., Kumar, P., Kumar, R., Kumar, S., Kuo, L., Kutynia, A., Kwang, S., Lackey, B. D., Lai, K. H., Landry, M., Lang, R. N., Lange, J., Lantz, B., Lanza, R. K., Lartaux-Vollard, A., Lasky, P. D., Laxen, M., Lazzarini, A., Lazzaro, C., Leaci, P., Leavey, S., Lee, C. H., Lee, H. K., Lee, H. M., Lee, H. W., Lee, K., Lehmann, J., Lenon, A., Leonardi, M., Leroy, N., Letendre, N., Levin, Y., Li, T. G. F., Libson, A., Littenberg, T. B., Liu, J., Lo, R. K. L., Lockerbie, N. A., London, L. T., Lord, J. E., Lorenzini, M., Loriette, V., Lormand, M., Losurdo, G., Lough, J. D., Lousto, C. O., Lovelace, G., Lück, H., Lumaca, D., Lundgren, A. P., Lynch, R., Ma, Y., Macfoy, S., Machenschalk, B., Macinnis, M., Macleod, D. M., Hernandez, I. Magaña, Magaña-Sandoval, F., Zertuche, L. Magaña, Magee, R. M., Majorana, E., Maksimovic, I., Man, N., Mandic, V., Mangano, V., Mansell, G. L., Manske, M., Mantovani, M., Marchesoni, F., Marion, F., Márka, S., Márka, Z., Markakis, C., Markosyan, A. S., Maros, E., Martelli, F., Martellini, L., Martin, I. W., Martynov, D. V., Mason, K., Masserot, A., Massinger, T. J., Masso-Reid, M., Mastrogiovanni, S., Matas, A., Matichard, F., Matone, L., Mavalvala, N., Mayani, R., Mazumder, N., Mccarthy, R., Mcclelland, D. E., Mccormick, S., Mcculler, L., Mcguire, S. C., Mcintyre, G., Mciver, J., Mcmanus, D. J., Mcrae, T., Mcwilliams, S. T., Meacher, D., Meadors, G. D., Meidam, J., Mejuto-Villa, E., Melatos, A., Mendell, G., Mercer, R. A., Merilh, E. L., Merzougui, M., Meshkov, S., Messenger, C., Messick, C., Metzdorff, R., Meyers, P. M., Mezzani, F., Miao, H., Michel, C., Middleton, H., Mikhailov, E. E., Milano, L., Miller, A. L., Miller, A., Miller, B. B., Miller, J., Millhouse, M., Minazzoli, O., Minenkov, Y., Ming, J., Mishra, C., Mitra, S., Mitrofanov, V. P., Mitselmakher, G., Mittleman, R., Moggi, A., Mohan, M., Mohapatra, S. R. P., Montani, M., Moore, B. C., Moore, C. J., Moraru, D., Moreno, G., Morriss, S. R., Mours, B., Mow-Lowry, C. M., Mueller, G., Muir, A. W., Mukherjee, Arunava, Mukherjee, D., Mukherjee, S., Mukund, N., Mullavey, A., Munch, J., Muniz, E. A. M., Murray, P. G., Napier, K., Nardecchia, I., Naticchioni, L., Nayak, R. K., Nelemans, G., Nelson, T. J. N., Neri, M., Nery, M., Neunzert, A., Newport, J. M., Newton, G., Ng, K. K. Y., Nguyen, T. T., Nichols, D., Nielsen, A. B., Nissanke, S., Nitz, A., Noack, A., Nocera, F., Nolting, D., Normandin, M. E. N., Nuttall, L. K., Oberling, J., Ochsner, E., Oelker, E., Ogin, G. H., Oh, J. J., Oh, S. H., Ohme, F., Oliver, M., Oppermann, P., Oram, Richard J., O'Reilly, B., Ormiston, R., Ortega, L. F., O'Shaughnessy, R., Ottaway, D. J., Overmier, H., Owen, B. J., Pace, A. E., Page, J., Page, M. A., Pai, A., Pai, S. A., Palamos, J. R., Palashov, O., Palomba, C., Pal-Singh, A., Pan, H., Pang, B., Pang, P. T. H., Pankow, C., Pannarale, F., Pant, B. C., Paoletti, F., Paoli, A., Papa, M. A., Paris, H. R., Parker, W., Pascucci, D., Pasqualetti, A., Passaquieti, R., Passuello, D., Patricelli, B., Pearlstone, B. L., Pedraza, M., Pedurand, R., Pekowsky, L., Pele, A., Penn, S., Perez, C. J., Perreca, A., Perri, L. M., Pfeiffer, H. P., Phelps, M., Piccinni, O. J., Pichot, M., Piergiovanni, F., Pierro, V., Pillant, G., Pinard, L., Pinto, I. M., Pitkin, M., Poggiani, R., Popolizio, P., Porter, E. K., Post, A., Powell, J., Prasad, J., Pratt, J. W. W., Predoi, V., Prestegard, T., Prijatelj, M., Principe, M., Privitera, S., Prix, R., Prodi, G. A., Prokhorov, L. G., Puncken, O., Punturo, M., Puppo, P., Pürrer, M., Qi, H., Qin, J., Qiu, S., Quetschke, V., Quintero, E. A., Quitzow-James, R., Raab, F. J., Rabeling, D. S., Radkins, H., Raffai, P., Raja, S., Rajan, C., Rakhmanov, M., Ramirez, K. E., Rapagnani, P., Raymond, V., Razzano, M., Read, J., Regimbau, T., Rei, L., Reid, S., Reitze, D. H., Rew, H., Reyes, S. D., Ricci, F., Ricker, P. M., Rieger, S., Riles, K., Rizzo, M., Robertson, N. A., Robie, R., Robinet, F., Rocchi, A., Rolland, L., Rollins, J. G., Roma, V. J., Romano, R., Romel, C. L., Romie, J. H., Rosińska, D., Ross, M. P., Rowan, S., Rüdiger, A., Ruggi, P., Ryan, K., Rynge, M., Sachdev, S., Sadecki, T., Sadeghian, L., Sakellariadou, M., Salconi, L., Saleem, M., Salemi, F., Samajdar, A., Sammut, L., Sampson, L. M., Sanchez, E. J., Sandberg, V., Sandeen, B., Sanders, J. R., Sassolas, B., Sathyaprakash, B. S., Saulson, P. R., Sauter, O., Savage, R. L., Sawadsky, A., Schale, P., Scheuer, J., Schmidt, E., Schmidt, J., Schmidt, P., Schnabel, R., Schofield, R. M. S., Schönbeck, A., Schreiber, E., Schuette, D., Schulte, B. W., Schutz, B. F., Schwalbe, S. G., Scott, J., Scott, S. M., Seidel, E., Sellers, D., Sengupta, A. S., Sentenac, D., Sequino, V., Sergeev, A., Shaddock, D. A., Shaffer, T. J., Shah, A. A., Shahriar, M. S., Shao, L., Shapiro, B., Shawhan, P., Sheperd, A., Shoemaker, D. H., Shoemaker, D. M., Siellez, K., Siemens, X., Sieniawska, M., Sigg, D., Silva, A. D., Singer, A., Singer, L. P., Singh, A., Singh, R., Singhal, A., Sintes, A. M., Slagmolen, B. J. J., Smith, B., Smith, J. R., Smith, R. J. E., Son, E. J., Sonnenberg, J. A., Sorazu, B., Sorrentino, F., Souradeep, T., Spencer, A. P., Srivastava, A. K., Staley, A., Steinke, M., Steinlechner, J., Steinlechner, S., Steinmeyer, D., Stephens, B. C., Stone, R., Strain, K. A., Stratta, G., Strigin, S. E., Sturani, R., Stuver, A. L., Summerscales, T. Z., Sun, L., Sunil, S., Sutton, P. J., Swinkels, B. L., Szczepańczyk, M. J., Tacca, M., Talukder, D., Tanner, D. B., Tápai, M., Taracchini, A., Taylor, J. A., Taylor, R., Theeg, T., Thomas, E. G., Thomas, M., Thomas, P., Thorne, K. A., Thorne, K. S., Thrane, E., Tiwari, S., Tiwari, V., Tokmakov, K. V., Toland, K., Tonelli, M., Tornasi, Z., Torrie, C. I., Töyrä, D., Travasso, F., Traylor, G., Trifirò, D., Trinastic, J., Tringali, M. C., Trozzo, L., Tsang, K. W., Tse, M., Tso, R., Tuyenbayev, D., Ueno, K., Ugolini, D., Unnikrishnan, C. S., Urban, A. L., Usman, S. A., Vahi, K., Vahlbruch, H., Vajente, G., Valdes, G., Vallisneri, M., Bakel, N. Van, Beuzekom, M. Van, Van Den Brand, J. F. J., Van Den Broeck, C., Vander-Hyde, D. C., Schaaf, L. Van Der, Heijningen, J. V. Van, Veggel, A. A. Van, Vardaro, M., Varma, V., Vass, S., Vasúth, M., Vecchio, A., Vedovato, G., Veitch, J., Veitch, P. J., Venkateswara, K., Venugopalan, G., Verkindt, D., Vetrano, F., Viceré, A., Viets, A. D., Vinciguerra, S., Vine, D. J., Vinet, J. -Y., Vitale, S., Vo, T., Vocca, H., Vorvick, C., Voss, D. V., Vousden, W. D., Vyatchanin, S. P., Wade, A. R., Wade, L. E., Wade, M., Walet, R., Walker, M., Wallace, L., Walsh, S., Wang, G., Wang, H., Wang, J. Z., Wang, M., Wang, Y. -F., Wang, Y., Ward, R. L., Warner, J., Was, M., Watchi, J., Weaver, B., Wei, L. -W., Weinert, M., Weinstein, A. J., Weiss, R., Wen, L., Wessel, E. K., Wessels, P., Westphal, T., Wette, K., Whelan, J. T., Whiting, B. F., Whittle, C., Williams, D., Williams, R. D., Williamson, A. R., Willis, J. L., Willke, B., Wimmer, M. H., Winkler, W., Wipf, C. C., Wittel, H., Woan, G., Woehler, J., Wofford, J., Wong, K. W. K., Worden, J., Wright, J. L., Wu, D. S., Wu, G., Yam, W., Yamamoto, H., Yancey, C. C., Yap, M. J., Yu, Hang, Yu, Haocun, Yvert, M., Zanolin, M., Zelenova, T., Zendri, J. -P., Zevin, M., Zhang, L., Zhang, M., Zhang, T., Zhang, Y. -H., Zhao, C., Zhou, M., Zhou, Z., Zhu, X. J., Zucker, M. E., Zweizig, J., Steeghs, D., Wang, L., The LIGO Scientific Collaboration, The Virgo Collaboration, Université de Lyon-Université de Lyon-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Collège de France (CdF (institution))-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Annecy de Physique des Particules ( LAPP/Laboratoire d'Annecy-le-Vieux de Physique des Particules ), Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Université Savoie Mont Blanc ( USMB [Université de Savoie] [Université de Chambéry] ) -Centre National de la Recherche Scientifique ( CNRS ), Laboratoire des matériaux avancés ( LMA ), Université Claude Bernard Lyon 1 ( UCBL ), Université de Lyon-Université de Lyon-Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Centre National de la Recherche Scientifique ( CNRS ) -Centre National de la Recherche Scientifique ( CNRS ), Laboratoire de l'Accélérateur Linéaire ( LAL ), Université Paris-Sud - Paris 11 ( UP11 ) -Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Centre National de la Recherche Scientifique ( CNRS ), AstroParticule et Cosmologie ( APC - UMR 7164 ), Centre National de la Recherche Scientifique ( CNRS ) -Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Observatoire de Paris-Université Paris Diderot - Paris 7 ( UPD7 ) -Commissariat à l'énergie atomique et aux énergies alternatives ( CEA ), Astrophysique Relativiste Théories Expériences Métrologie Instrumentation Signaux ( ARTEMIS ), Université Nice Sophia Antipolis ( UNS ), Université Côte d'Azur ( UCA ) -Université Côte d'Azur ( UCA ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Observatoire de la Côte d'Azur, Université Côte d'Azur ( UCA ) -Centre National de la Recherche Scientifique ( CNRS ), Institut de Physique de Rennes ( IPR ), Université de Rennes 1 ( UR1 ), Université de Rennes ( UNIV-RENNES ) -Université de Rennes ( UNIV-RENNES ) -Centre National de la Recherche Scientifique ( CNRS ), Laboratoire Kastler Brossel ( LKB (Lhomond) ), Fédération de recherche du Département de physique de l'Ecole Normale Supérieure - ENS Paris ( FRDPENS ), Centre National de la Recherche Scientifique ( CNRS ) -École normale supérieure - Paris ( ENS Paris ) -Centre National de la Recherche Scientifique ( CNRS ) -École normale supérieure - Paris ( ENS Paris ) -Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Centre National de la Recherche Scientifique ( CNRS ), (Astro)-Particles Physics, Massachusetts Institute of Technology. Department of Physics, LIGO (Observatory : Massachusetts Institute of Technology), MIT Kavli Institute for Astrophysics and Space Research, Aggarwal, Nancy, Barsotti, Lisa, Biscans, Sebastien, Buikema, Aaron, Donovan, Frederick J, Eisenstein, Robert Alan, Essick, Reed Clasey, Evans, Matthew J, Fernandez Galiana, Alvaro-Miguel, Fritschel, Peter K, Gras, Slawomir, Katsavounidis, Erotokritos, Kontos, Antonios, Lanza Jr, Robert K, Libson, Adam A., Lynch, Ryan Christopher, MacInnis, Myron E, Martynov, Denis, Mason, Kenneth R, Matichard, Fabrice, Mavalvala, Nergis, McCuller, Lee P, Miller, John, Mittleman, Richard K, Ray Pitambar Mohapatra, Satyanarayan, Oelker, Eric Glenn, Shoemaker, David H, Tse, Maggie, Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, and PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)

Subjects
accretion, accretion disks, gravitational waves, stars: neutron, X-rays: binaries, Astronomy and Astrophysics, Space and Planetary Science, Astronomy, [ PHYS.ASTR ] Physics [physics]/Astrophysics [astro-ph], accretion, accretion disk, spin, 01 natural sciences, General Relativity and Quantum Cosmology, neutron, accretion, accretion,accretion disks, Range (statistics), LIGO, neutron star, GeneralLiterature_REFERENCE(e.g.,dictionaries,encyclopedias,glossaries), 010303 astronomy & astrophysics, gravitational wave, QC, QB, Physics, astro-ph.HE, High Energy Astrophysical Phenomena (astro-ph.HE), accretion disks, SDG 10 - Reduced Inequalities, X-rays: binarie, Amplitude, X-ray: binary, Astrophysics - High Energy Astrophysical Phenomena, stars, FOS: Physical sciences, General Relativity and Quantum Cosmology (gr-qc), 1ST SEARCH, Accretion, neutron [stars], 0103 physical sciences, Continuous signal, Orbital elements, Cross-correlation, 010308 nuclear & particles physics, Gravitational wave, Physique, gravitational radiation, Astronomy and Astrophysic, gravitational radiation detector, Computational physics, coherence, detector: sensitivity, Neutron star, Physics and Astronomy, gravitational radiation: emission, RADIATION, binaries [X-rays], neutron, X-rays: binaries [accretion, accretion disks, gravitational waves, stars], [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

We present the results of a semicoherent search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1, using data from the first Advanced LIGO observing run. The search method uses details of the modeled, parametrized continuous signal to combine coherently data separated by less than a specified coherence time, which can be adjusted to trade off sensitivity against computational cost. A search was conducted over the frequency range 25-2000 Hz, spanning the current observationally constrained range of binary orbital parameters. No significant detection candidates were found, and frequency-dependent upper limits were set using a combination of sensitivity estimates and simulated signal injections. The most stringent upper limit was set at 175 Hz, with comparable limits set across the most sensitive frequency range from 100 to 200 Hz. At this frequency, the 95% upper limit on the signal amplitude h0 is 2.3 × 10-25 marginalized over the unknown inclination angle of the neutron star's spin, and 8.0 × 10-26 assuming the best orientation (which results in circularly polarized gravitational waves). These limits are a factor of 3-4 stronger than those set by other analyses of the same data, and a factor of ∼ 7 stronger than the best upper limits set using data from Initial LIGO science runs. In the vicinity of 100 Hz, the limits are a factor of between 1.2 and 3.5 above the predictions of the torque balance model, depending on the inclination angle; if the most likely inclination angle of 44° is assumed, they are within a factor of 1.7., 0, info:eu-repo/semantics/published

Published
2017

16. The fine line between total and partial tidal disruption events

Author

Alessandro Lupi, Sergio Campana, Enrico Ramirez-Ruiz, Deborah Mainetti, Monica Colpi, James Guillochon, Eric R. Coughlin, Institut d'Astrophysique de Paris (IAP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), ITA, USA, FRA, Mainetti, D, Lupi, A, Campana, S, Colpi, M, Coughlin, E, Guillochon, J, Ramirez Ruiz, E, Institut d'Astrophysique de Paris ( IAP ), and Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS )

Subjects
Critical distance, [ PHYS.ASTR ] Physics [physics]/Astrophysics [astro-ph], Astrophysics::High Energy Astrophysical Phenomena, black hole physics, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Star (graph theory), Fine line, 01 natural sciences, methods: numerical, Black hole physic, General Relativity and Quantum Cosmology, Accretion, accretion disk, Accretion disc, accretion, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Finite mass, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Accretion, accretion disks, Black hole physics, Galaxies: nuclei, Hydrodynamics, Methods: numerical, Astronomy and Astrophysics, Space and Planetary Science, Accretion (meteorology), 010308 nuclear & particles physics, Hydrodynamic, Astronomy and Astrophysic, Galaxy, Polytrope, hydrodynamics, Astrophysics::Earth and Planetary Astrophysics, galaxies: nuclei, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

Flares from tidal disruption events are unique tracers of quiescent black holes at the centre of galaxies. The appearance of these flares is very sensitive to whether the star is totally or partially disrupted, and in this paper we seek to identify the critical distance of the star from the black hole (r_d) that enables us to distinguish between these two outcomes. We perform here Mesh-free Finite Mass, traditional, and modern Smoothed Particle Hydrodynamical simulations of star-black hole close encounters, with the aim of checking if the value of r_d depends on the simulation technique. We find that the critical distance (or the so-called critical disruption parameter beta_d) depends only weakly on the adopted simulation method, being beta_d=0.92\pm 0.02 for a gamma=5/3 polytrope and beta_d=2.01\pm 0.01 for a gamma=4/3 polytrope., 8 pages, 8 figures, 2 tables; accepted to A&A

Published
2017

17. A broadband spectral analysis of 4U 1702-429 using XMM-Newton and BeppoSAX data

Author

A. Segreto, T. Di Salvo, Alessandro Riggio, N. D'Amico, Andrea Santangelo, Andrea Sanna, Angelo Gambino, S. M. Mazzola, M. Del Santo, R. Iaria, Luciano Burderi, Mazzola, S.M., Iaria, R., Di Salvo, T., Del Santo, M., Sanna, A., Gambino, A.F., Riggio, A., Segreto, A., Burderi, L., Santangelo, A., and D'Amico, N.

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, X-rays: Binarie, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Binary number, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Corona, Stars: neutron, Spectral line, Neutron star, Accretion, accretion disk, Space and Planetary Science, Ionization, Stars: Individual: 4U 1702-429, 0103 physical sciences, Reflection (physics), Black-body radiation, Astrophysics - High Energy Astrophysical Phenomena, Low Mass, 010303 astronomy & astrophysics
Abstract

Most of the X-ray binary systems containing neutron stars classified as Atoll sources show two different spectral states, called soft and hard. Moreover, a large number of these systems show a reflection component relativistically smeared in their spectra, which gives information on the innermost region of the system. Our aim is to investigate the poorly studied broadband spectrum of the low mass X-ray binary system 4U 1702-429, which was recently analysed combining XMM-Newton and INTEGRAL data. The peculiar value of the reflection fraction brought us to analyse further broadband spectra of 4U 1702-429. We re-analysed the spectrum of the XMM-Newton/INTEGRAL observation of 4U 1702-429 in the 0.3-60 keV energy range and we extracted three 0.1-100 keV spectra of the source analysing three observations collected with the BeppoSAX satellite. We find that the XMM-Newton/INTEGRAL spectrum is well fitted using a model composed of a disc blackbody plus a Comptonised component and a smeared reflection component. We used the same spectral model for the BeppoSAX spectra, finding out that the addition of a smeared reflection component is statistically significant. The best-fit values of the parameters are compatible to each other for the BeppoSAX spectra. We find that the reflection fraction is $0.05^{+0.03}_{-0.01}$ for the XMM-Newton/INTEGRAL spectrum and between 0.15 and 0.4 for BeppoSAX ones. The relative reflection fraction and the ionisation parameter are incompatible between the XMM-Newton/INTEGRAL and the BeppoSAX observations and the characteristics of the Comptonising corona suggest that the source was in a soft state in the former observation and in a hard state in the latter., 10 pages, 14 figures, submitted to A&A

Published
2019

18. A numerical code to study the variability of Blazar emission

Author

Tramacere, A. and Tosti, G.

Subjects
*BL Lacertae objects, *RADIO sources (Astronomy), *ACTIVE galaxies, *ELECTROMAGNETISM, *ASTRONOMY
Abstract

We present a numerical code, written in C, which can be used to simulate or to analyze the emission of Blazars over the entire electromagnetic spectrum. Our code can reproduce: Synchrotron emission, Inverse Compton emission (IC) (Thomson & Klein-Nishina regime), External Compton emission (EC), accretion disk variability using a Cellular Automata (CA) algorithm, temporal evolution of the emitting plasma energy distribution, flaring phenomena, light curves in the rest and in the observer frame (taking account for time crossing effects). [Copyright &y& Elsevier]

Published
2003
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19. Hydrodynamic Modeling of Accretion Impacts in Classical T Tauri Stars: Radiative Heating of the Pre-shock Plasma

Author

Costanza Argiroffi, Rosaria Bonito, Giovanni Peres, G. Costa, Salvatore Orlando, ITA, Costa, G., Orlando, S., Peres, G., Argiroffi, C., and Bonito, R.

Subjects
Shock wave, Radiative cooling, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Accretion, accretion disk, Settore FIS/05 - Astronomia E Astrofisica, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, X-rays: star, Irradiation, Emission spectrum, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, Physics, 010308 nuclear & particles physics, Astronomy and Astrophysics, Hydrodynamic, Plasma, Astronomy and Astrophysic, Thermal conduction, Accretion (astrophysics), T Tauri star, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Stars: pre-main sequence, Astrophysics::Earth and Planetary Astrophysics
Abstract

Context. It is generally accepted that, in classical T Tauri stars, the plasma from the circumstellar disc accretes onto the stellar surface with free-fall velocity and the impact generates a shock. The impact region is expected to contribute to emission in different spectral bands; many studies have confirmed that the X-rays arise from the post-shock plasma but, otherwise, there are no studies in the literature investigating the origin of the observed UV emission which is apparently correlated to accretion. Aims: We investigated the effect of radiative heating of the infalling material by the post-shock plasma at the base of the accretion stream, with the aim to identify in which region a significant part of the UV emission originates. Methods: We developed a one-dimensional hydrodynamic model describing the impact of an accretion stream onto the stellar surface; the model takes into account the gravity, the radiative cooling of an optically thin plasma, the thermal conduction, and the heating due to absorption of X-ray radiation. The latter term represents the heating of the infalling plasma due to the absorption of X-rays emitted from the post-shock region. Results: We found that the radiative heating of the pre-shock plasma plays a non-negligible role in the accretion phenomenon. In particular, the dense and cold plasma of the pre-shock accretion column is gradually heated up to a few 105K due to irradiation of X-rays arising from the shocked plasma at the impact region. This heating mechanism does not affect significantly the dynamics of the post-shock plasma. On the other hand, a region of radiatively heated gas (that we consider a precursor) forms in the unshocked accretion column and contributes significantly to UV emission. Our model naturally reproduces the luminosity of UV emission lines correlated to accretion and shows that most of the UV emission originates from the precursor....

Published
2016

20. Angular momentum, accretion and radial flows in chemodynamical models of spiral galaxies

Author

Pezzulli, G., Fraternali, F., Pezzulli, G., Fraternali, F., and Astronomy

Subjects
accretion disks, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astronomy and Astrophysic, accretion, accretion disk, Astrophysics - Astrophysics of Galaxies, Galaxy: abundance, accretion, galaxies: abundance, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Galaxy: abundances, Astrophysics::Solar and Stellar Astrophysics, galaxies: abundances, intergalactic medium, Astrophysics::Earth and Planetary Astrophysics, galaxies: evolution, galaxies: ISM, Astrophysics::Galaxy Astrophysics
Abstract

Gas accretion and radial flows are key ingredients of the chemical evolution of spiral galaxies. They are also tightly linked to each other (accretion drives radial flows, due to angular momentum conservation) and should therefore be modelled simultaneously. We summarise an algorithm that can be used to consistently compute accretion profiles, radial flows and abundance gradients under quite general conditions and we describe illustrative applications to the Milky Way. We find that gas-phase abundance gradients strongly depend on the angular momentum of the accreting material and, in the outer regions, they are significantly affected by the choice of boundary conditions., 4 pages, 2 figures. Proceedings of the 592 WE-Heraeus Seminar. To appear in Astronomische Nachricthen, special issue "Reconstructing the Milky Way's history: spectroscopic surveys, asteroseismology and chemodynamical models", Guest Editors C. Chiappini, J. Montalban and M. Steffen

Published
2016

21. Short Gamma-Ray Bursts from the Merger of Two Black Holes

Author

Rosalba Perna, Bruno Giacomazzo, Davide Lazzati, Perna, R, Lazzati, D, and Giacomazzo, B

Subjects
Astrophysics::High Energy Astrophysical Phenomena, gamma-ray burst: general, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, general [gamma-ray burst], accretion, accretion disk, 01 natural sciences, massive [stars], accretion, 0103 physical sciences, general, gravitational waves, stars black holes, stars: massive, Space and Planetary Science, Astronomy and Astrophysics [accretion, accretion disks, gamma-ray burst], stars black hole, 010303 astronomy & astrophysics, gravitational wave, accretion disk, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, Gravitational wave, accretion disks, Astronomy and Astrophysics, Accretion (astrophysics), Black hole, Neutron star, Supernova, Stars, Astrophysics::Earth and Planetary Astrophysics, Gamma-ray burst, Astrophysics - High Energy Astrophysical Phenomena, Fermi Gamma-ray Space Telescope
Abstract

Short Gamma-Ray Bursts (GRBs) are explosions of cosmic origin believed to be associated with the merger of two compact objects, either two neutron stars, or a neutron star and a black hole. The presence of at least one neutron star has long been thought to be an essential element of the model: its tidal disruption provides the needed baryonic material whose rapid accretion onto the post-merger black hole powers the burst. The recent tentative detection by the Fermi satellite of a short GRB in association with the gravitational wave signal GW150914 produced by the merger of two black holes has challenged this standard paradigm. Here we show that the evolution of two high-mass, low-metallicity stars with main sequence rotational speeds a few tens of percent of the critical speed eventually undergoing a weak supernova explosion {\em can} produce a short gamma-ray burst. The outer layers of the envelope of the last exploding star remain bound and circularize at large radii. With time, the disk cools and becomes neutral, suppressing the magneto-rotational instability, and hence the viscosity. The disk remains 'long-lived dead' until tidal torques and shocks during the pre-merger phase heat it up and re-ignite accretion, rapidly consuming the disk and powering the short gamma-ray burst., Matches version accepted to ApJL

Published
2016

22. A TEST of the NATURE of the FE K LINE in the NEUTRON STAR LOW-MASS X-RAY BINARY SERPENS X-1

Author

Jeroen Homan, Luciano Burderi, Sudip Bhattacharyya, Tiziana Di Salvo, Chia-Ying Chiang, Michael Parker, Jon M. Miller, Elise Egron, R. Iaria, Antonino D'Ai, Edward M. Cackett, Didier Barret, Dacheng Lin, Andrew C. Fabian, M. Coleman Miller, Chiang, C., Cackett, E., Miller, J., Barret, D., Fabian, A., D'Aì, A., Parker, M., Bhattacharyya, S., Burderi, L., Di Salvo, T., Egron, E., Homan, J., Iaria, R., Lin, D., Miller, M., ITA, USA, GBR, FRA, and IND

Subjects
Serpens, Astrophysics::High Energy Astrophysical Phenomena, X-ray binary, FOS: Physical sciences, Astrophysics, accretion, accretion disk, 01 natural sciences, Spectral line, stars: neutron, Settore FIS/05 - Astronomia E Astrofisica, 0103 physical sciences, Emission spectrum, 010303 astronomy & astrophysics, Line (formation), High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, Astronomy and Astrophysics, profiles, X-rays: binaries, Space and Planetary Science [accretion, accretion disks, line], Astronomy and Astrophysic, K-line, X-rays: binarie, Black hole, Neutron star, line: profile, Space and Planetary Science, Astrophysics - High Energy Astrophysical Phenomena
Abstract

Broad Fe K emission lines have been widely observed in the X-ray spectra of black hole systems, and in neutron star systems as well. The intrinsically narrow Fe K fluorescent line is generally believed to be part of the reflection spectrum originating in an illuminated accretion disk, and broadened by strong relativistic effects. However, the nature of the lines in neutron star LMXBs has been under debate. We therefore obtained the longest, high-resolution X-ray spectrum of a neutron star LMXB to date with a 300 ks Chandra HETGS observation of Serpens X-1. The observation was taken under the "continuous clocking" mode and thus free of photon pile-up effects. We carry out a systematic analysis and find that the blurred reflection model fits the Fe line of Serpens X-1 significantly better than a broad Gaussian component does, implying that the relativistic reflection scenario is much preferred. Chandra HETGS also provides highest spectral resolution view of the Fe K region and we find no strong evidence for additional narrow lines., Accepted for publication in ApJ

Published
2016

23. NuSTAR reveals the extreme properties of the super-Eddington accreting supermassive black hole in PG 1247+267

Author

Duncan Farrah, Franz E. Bauer, M. Cappi, W. N. Brandt, W. W. Zhang, Giorgio Lanzuisi, M. Dadina, Enrico Piconcelli, Fausto Vagnetti, Andrea Comastri, C. J. Hailey, William W. Craig, S. E. Boggs, Fiona A. Harrison, Giorgio Matt, Claudio Ricci, A. C. Fabian, Dom Walton, Andrea Marinucci, F. E. Christensen, Michele Perna, S. Puccetti, David R. Ballantyne, Alberto Masini, D. Stern, C. Vignali, Cristian Saez, B. Luo, Marcella Brusa, Lanzuisi, G., Perna, M., Comastri, A., Cappi, M., Dadina, M., Marinucci, Andrea, Masini, A., Matt, Giorgio, Vagnetti, F., Vignali, C., Ballantyne, D. R., Bauer, F. E., Boggs, S. E., Brandt, W. N., Brusa, M., Christensen, F. E., Craig, W. W., Fabian, A. C., Farrah, D., Hailey, C. J., Harrison, F. A., Luo, B., Piconcelli, E., Puccetti, S., Ricci, C., Saez, C., Stern, D., Walton, D. J., Zhang, W. W., Marinucci, A., Matt, G., Ballantyne, D.R., Bauer, F.E., Boggs, S.E., Brandt, W.N., Christensen, F.E., Craig, W.W., Fabian, A.C., Hailey, C.J., Harrison, F.A., Walton, D.J., and Zhang, W.W.

Subjects
Accretion, active [Galaxies], Astrophysics::High Energy Astrophysical Phenomena, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Power law, Relativistic disk, Quasars: individual: PG 1247+267, Accretion, accretion disk, Settore FIS/05 - Astronomia e Astrofisica, individual: PG 1247+267 [Quasars], Ionization, 0103 physical sciences, Cutoff, Emission spectrum, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Galaxies: nuclei, Physics, 010308 nuclear & particles physics, Astronomy and Astrophysics, Quasar, Plasma, Galaxies: active, Astronomy and Astrophysic, Redshift, Space and Planetary Science, nuclei [Galaxies], Accretion disks
Abstract

PG1247+267 is one of the most luminous known quasars at z similar to 2 and is a strongly super-Eddington accreting supermassive black hole (SMBH) candidate. We obtained NuSTAR data of this intriguing source in December 2014 with the aim of studying its high-energy emission, leveraging the broad band covered by the new NuSTAR and the archival XMM-Newton data. Several measurements are in agreement with the super-Eddington scenario for PG1247+267: the soft power law (Gamma = 2.3 +/- 0.1); the weak ionized Fe emission line; and a hint of the presence of outflowing ionized gas surrounding the SMBH. The presence of an extreme reflection component is instead at odds with the high accretion rate proposed for this quasar. This can be explained with three different scenarios; all of them are in good agreement with the existing data, but imply very different conclusions: i) a variable primary power law observed in a low state, superimposed on a reflection component echoing a past, higher flux state; ii) a power law continuum obscured by an ionized, Compton thick, partial covering absorber; and iii) a relativistic disk reflector in a lamp-post geometry, with low coronal height and high BH spin. The first model is able to explain the high reflection component in terms of variability. The second does not require any reflection to reproduce the hard emission, while a rather low high-energy cutoff of similar to 100 keV is detected for the first time in such a high redshift source. The third model require a face-on geometry, which may affect the SMBH mass and Eddington ratio measurements. Deeper X-ray broad-band data are required in order to distinguish between these possibilities.

Published
2016

24. XMMSL1J063045.9-603110: a tidal disruption event fallen into the back burner

Author

Sergio Campana, Monica Colpi, Deborah Mainetti, ITA, Mainetti, D, Campana, S, and Colpi, M

Subjects
Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, X-rays:galaxie, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Compact star, 01 natural sciences, law.invention, Tidal disruption event, Accretion, accretion disk, law, 0103 physical sciences, Tidal force, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, galaxies:dwarf, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Galaxies: dwarf, 010308 nuclear & particles physics, Astronomy and Astrophysics, Accretion (astrophysics), Galaxy, Black hole, Space and Planetary Science, Globular cluster, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, X-rays: galaxie, Flare
Abstract

Black holes at the centre of quiescent galaxies can be switched on when they accrete gas that is gained from stellar tidal disruptions. A star approaching a black hole on a low angular momentum orbit may be ripped apart by tidal forces, which triggers raining down of a fraction of stellar debris onto the compact object through an accretion disc and powers a bright flare. In this paper we discuss XMMSL1J063045.9-603110 as a candidate object for a tidal disruption event. The source has recently been detected to be bright in the soft X-rays during an XMM-Newton slew and later showed an X-ray flux decay by a factor of about 10 in twenty days. We analyse XMM-Newton and Swift data. XMMSL1J063045.9-603110 shows several features typical of tidal disruption events: the X-ray spectrum shows the characteristics of a spectrum arising from a thermal accretion disc, the flux decay follows a t^-5/3 law, and the flux variation is > 350. Optical observations testify that XMMSL1J063045.9-603110 is probably associated with an extremely small galaxy or even a globular cluster, which suggests that intermediate-mass black holes are located in the cores of (at least) some of them., 8 pages, 4 figures; accepted to A&A

Published
2016

25. Retrograde binaries of massive black holes in circumbinary accretion discs

Author

Massimo Dotti, Cristián Maureira-Fredes, Monica Colpi, Pau Amaro-Seoane, Amaro Seoane, P, Maureira Fredes, C, Dotti, M, and Colpi, M

Subjects
Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Binary number, Astrophysics, 01 natural sciences, Gravitation, General Relativity and Quantum Cosmology, Accretion, accretion disk, Accretion disc, 0103 physical sciences, Roche lobe, Methods: analytical, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Methods: numerical, 010308 nuclear & particles physics, Astronomy and Astrophysics, Hydrodynamic, Astronomy and Astrophysic, Astrophysics - Astrophysics of Galaxies, Black hole, Density distribution, Drag, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics::Earth and Planetary Astrophysics, Circumbinary planet, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

We explore the hardening of a massive black hole binary embedded in a circum-binary gas disc when the binary and the gas are coplanar and the gas is counter-rotating. The secondary black hole, revolving in the direction opposite to the gas, experiences a drag from gas-dynamical friction and from direct accretion of part of it. Using two-dimensional (2D) hydrodynamical grid simulations we investigate the effect of changing the accretion prescriptions on the dynamics of the secondary black hole which in turn affect the binary hardening and eccentricity evolution. We find that realistic accretion prescriptions lead to results that differ from those inferred assuming accretion of all the gas within the Roche Lobe of the secondary black hole. Different accretion prescriptions result in different disc's surface densities which alter the black hole's dynamics back. Full 3D SPH realizations of a number of representative cases, run over a shorter interval of time, validate the general trends observed in the less computationally demanding 2D simulations. Initially circular black hole binaries increase only slightly their eccentricity which then oscillates around small values (, abridged. Accepted for publication A&A

Published
2016

26. Broadband observations of the X-ray burster 4U1705-44 with Beppo SAX

Author

P. Kaaret, T. Di Salvo, R. Iaria, E. Egron, Andrea Santangelo, B. Mück, S. Piraino, Antonino D'Ai, Piraino, S., Santangelo, A., Mück, B., Kaaret, P., Di Salvo, T., D'Aì, A., Iaria, R., Egron, E., ITA, USA, and DEU

Subjects
X-ray burster, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Context (language use), Astrophysics, X-rays: general, 01 natural sciences, Spectral line, Accretion, accretion disk, Stars: individual: 4U 1705-44, Settore FIS/05 - Astronomia E Astrofisica, 0103 physical sciences, Black-body radiation, X-rays: star, 010303 astronomy & astrophysics, Line (formation), High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Accretion (meteorology), 010308 nuclear & particles physics, Astronomy and Astrophysics, Astronomy and Astrophysic, X-rays: binarie, Stars: neutron, Neutron star, Space and Planetary Science, Reflection (physics), individual: 4U 1705-44, X-rays: binaries, X-rays: stars, Space and Planetary Science [Accretion, accretion disks, Stars], Astrophysics - High Energy Astrophysical Phenomena
Abstract

4U 1705-44 is one of the most-studied type I X-ray burster and Atoll sources. This source represents a perfect candidate to test different models proposed to self-consistently track the physical changes occurring between different spectral states because it shows clear spectral state transitions. The broadband coverage, the sensitivity and energy resolution of the BeppoSAX satellite offers the opportunity to disentangle the components that form the total X-ray spectrum and to study their changes according to the spectral state. Using two BeppoSAX observations carried out in August and October 2000, respectively, for a total effective exposure time of about 100 ks, we study the spectral evolution of the source from a soft to hard state. Energy spectra are selected according to the source position in the color-color diagram (CCD) Results. We succeeded in modeling the spectra of the source using a physical self-consistent scenario for both the island and banana branches (the double Comptonization scenario). The components observed are the soft Comptonization and hard Comptonization, the blackbody, and a reflection component with a broad iron line. When the source moves from the banana state to the island state, the parameters of the two Comptonization components change significantly and the blackbody component becomes too weak to be detected. We interpret the soft Comptonization component as emission from the hot plasma surrounding the neutron star, hard Comptonization as emission from the disk region, and the blackbody component as emission from the inner accretion disk. The broad feature in the iron line region is compatible with reflection from the inner accretion disk., Comment: 8 pages, 10 figures, accepted for publication by A&A

Published
2016

27. High-energy monitoring of Seyfert galaxies: The case of NGC 4593

Author

Ursini, F., Petrucci, P. -O., Matt, G., Bianchi, S., Cappi, M., De Marco, B., De Rosa, A., Malzac, J., Ponti, G., Ursini, Francesco, Petrucci, P. O., Matt, Giorgio, Bianchi, Stefano, Cappi, M., De Marco, B., De Rosa, A., Malzac, J., Ponti, G., Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Université Toulouse III - Paul Sabatier (UT3), and Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), galaxie [X-rays], Seyfert [Galaxies], Accretion, accretion disk, active [Galaxies], Space and Planetary Science, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, individuals (NGC 4593) [X-rays], content, Astronomy and Astrophysic, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

We discuss preliminary results from a joint XMM-Newton and NuSTAR monitoring program on the active galactic nucleus NGC 4593, consisting of 5x20 ks observations, spaced by two days, performed in January 2015. The source is found to be variable, both in flux and spectral shape, on time scales as short as a few ks. The spectrum clearly softens when the source brightens. A simple timing analysis suggests the presence of a variable soft excess that correlates with the primary continuum., Proceedings of the XMM Science Workshop 2015; to appear in Astronomische Nachrichten

Published
2016

28. Effect of magnetic braking on circumstellar disk formation in a strongly magnetized cloud

Author

Tomoaki Matsumoto, Masahiro N. Machida, and Shu-ichiro Inutsuka

Subjects
Physics, Angular momentum, Astrophysics::High Energy Astrophysical Phenomena, Stars: formation, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Accretion (astrophysics), Magnetic field, Interstellar medium, Accretion, accretion disk, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Protostar, Astrophysics::Solar and Stellar Astrophysics, Outflow, Astrophysics::Earth and Planetary Astrophysics, Magnetohydrodynamics, Magnetohydrodynamics: MHD, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, Stars: magnetic fields, Envelope (waves)
Abstract

Using resistive magnetohydrodynamics simulation, we investigate circumstellar disk formation in a strongly magnetized cloud. As the initial state, an isolated cloud core embedded in a low-density interstellar medium with a uniform magnetic field is adopted. The cloud evolution is calculated until almost all gas inside the initial cloud falls onto either the circumstellar disk or a protostar, and a part of the gas is ejected into the interstellar medium by the protostellar outflow driven by the circumstellar disk. In the early main accretion phase, the disk size is limited to \sim 10 AU because the angular momentum of the circumstellar disk is effectively transferred by both magnetic braking and the protostellar outflow. In the later main accretion phase, however, the circumstellar disk grows rapidly and exceeds 100 AU by the end of the main accretion phase. This rapid growth of the circumstellar disk is caused by the depletion of the infalling envelope, while magnetic braking is effective when the infalling envelope is more massive than the circumstellar disk. The infalling envelope cannot brake the circumstellar disk when the latter is more massive than the former. In addition, the protostellar outflow weakens and disappears in the later main accretion phase, because the outflow is powered by gas accretion onto the circumstellar disk. Although the circumstellar disk formed in a magnetized cloud is considerably smaller than that in an unmagnetized cloud, a circumstellar disk exceeding 100 AU can form even in a strongly magnetized cloud., 39 pages, 13 figures, accepted for publication in PASJ. For high resolution figures see http://www2-tap.scphys.kyoto-u.ac.jp/~machidam/astro-ph/Magbraking.pdf

Published
2011

29. BeppoSAX observation of 4U 1705-44: detection of hard X-ray emission in the soft state

Author

Andrea Santangelo, Luciano Burderi, S. Piraino, P. Kaaret, Dieter Horns, R. Iaria, T. Di Salvo, PIRAINO S, SANTANGELO A, DI SALVO T, KAARET P, HORNS D, IARIA R, and BURDERI L

Subjects
Physics, Photon, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), stars : individual : 4U 1705-44, X-ray, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, accretion, accretion disk, stars : neutron, Power law, K-line, Soft state, Space and Planetary Science, X-rays : star, Electron temperature, Black-body radiation, Emission spectrum, individual : 4U 1705-44, X-rays : stars, X-rays : binaries, X-rays : general [accretion, accretion disks, stars], X-rays : binarie, X-rays : general
Abstract

4U 1705-44 is one of the best studied type I X-ray burster and atoll sources. Since it covers a wide range in luminosity (from a few to 50 x 10^{36} erg s^{-1}) and shows clear spectral state transitions, it represents a good laboratory to test the accretion models proposed for atoll sources. We analysed the energy spectrum accumulated with BeppoSAX observations (43.5 ksec) in August 2000 when the source was in a soft spectral state. The continuum of the wide band energy spectrum is well described by the sum of a blackbody (kT_{bb}~0.56 keV) and a Comptonized component (seed-photon temperature kT_W~1 keV, electron temperature kT_e~2.7 keV, and optical depth ~11). A hard tail was detected at energies above ~25 keV. The latter can be modeled by a power law having a photon index ~2.9 which contributes ~11% of the total flux in the range 0.1-200 keV. A broad emission line, possibly from a relativistic accretion disk, models the feature in the Fe K line region of the spectrum. This is the first time that a high energy tail has been observed during a soft state of the source., 4 pages,3 figures. Accepted for publication as a Letter to the Editor in A&A

Published
2007

30. The coronal parameters of local Seyfert galaxies

Author

Marinucci, A., Tortosa, A., Marinucci, A., and Tortosa, A.

Subjects
galaxie [X-rays], High Energy Astrophysical Phenomena (astro-ph.HE), Seyfert [Galaxies], active [Galaxies], Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astronomy and Astrophysic, Accretion, accretion disk, Space and Planetary Science, nuclei [Galaxies], Astrophysics::Solar and Stellar Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics::Galaxy Astrophysics
Abstract

One of the open problems for AGN is the nature of the primary X-ray emission: it is likely due to Comptonization of soft UV photons, but the optical depth and temperature of the emitting corona were largely unknown before the launch of the Nuclear Spectroscopic Telescope Array (NuSTAR). It is the first focusing hard X-ray telescope on orbit, 100 times more sensitive in the 10-79 keV band compared to previous observatories, enabling the study of AGN at high energies with high precision. We present and discuss the results on the hot corona parameters of Active Galactic Nuclei that have been recently measured with NuSTAR (often in coordination with XMM-Newton, Suzaku or Swift) with unprecedented accuracy, in a number of local Seyfert galaxies., 6 pages, 3 figures, accepted for publication on Astronomische Nachrichten/Astronomical Notes, proceedings of "The Extremes of Black Hole Accretion"

Published
2015

31. High ionisation absorption in low mass X-ray binaries

Author

PONTI, GABRIELE, Bianchi, S., Muñoz-Darias, T., De, K., Fender, R., Merloni, A., Ponti, G, Bianchi, Stefano, Muñoz Darias, T., De, K., Fender, R., and Merloni, A.

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), binarie [X-rays], Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astronomy and Astrophysic, individuals (AX J1745.6-2901, EXO0748-676) [X-rays], spectroscopic [Techniques], Accretion, accretion disk, Space and Planetary Science, Astrophysics::Solar and Stellar Astrophysics, winds, outflow [Stars], Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics::Galaxy Astrophysics
Abstract

The advent of the new generation of X-ray telescopes yielded a significant step forward in our understanding of ionised absorption generated in the accretion discs of X-ray binaries. It has become evident that these relatively weak and narrow absorption features, sporadically present in the X-ray spectra of some systems, are actually the signature of equatorial outflows, which might carry away more matter than that being accreted. Therefore, they play a major role in the accretion phenomenon. These outflows (or ionised atmospheres) are ubiquitous during the softer states but absent during the power-law dominated, hard states, suggesting a strong link with the state of the inner accretion disc, presence of the radio-jet and the properties of the central source. Here, we discuss the current understanding of this field., Accepted for publication in Astronomical Notes (Proceedings of "The Extremes of Black Hole Accretion" workshop, held at ESAC, Madrid, in June 2015)

Published
2015

32. Pan-STARRS1 variability of XMM-COSMOS AGN. II. Physical correlations and power spectrum analysis

Author

Roberto P. Saglia, Giorgio Lanzuisi, Kirpal Nandra, Gabriele Ponti, Mara Salvato, Benny Trakhtenbrot, T. Simm, Ralf Bender, Simm, T., Salvato, M., Saglia, R., Ponti, G., Lanzuisi, G., Trakhtenbrot, B., Nandra, K., and Bender, R.

Subjects
Active galactic nucleus, Hubble Deep Field, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Luminosity, Black hole physic, Accretion, accretion disk, 0103 physical sciences, 010303 astronomy & astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Astronomy and Astrophysics, Quasar, Galaxies: active, Astronomy and Astrophysic, Light curve, Astrophysics - Astrophysics of Galaxies, Redshift, Black hole, Quasars: general, Amplitude, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics - High Energy Astrophysical Phenomena, X-rays: galaxie, Methods: data analysi
Abstract

[Abbreviated] We search for scaling relations between the fundamental AGN parameters and rest-frame UV/optical variability properties for a sample of $\sim$90 X-ray selected AGNs covering a wide redshift range from the XMM-COSMOS survey, with optical light curves in four bands provided by the Pan-STARRS1 (PS1) Medium Deep Field 04 survey. To estimate the variability amplitude we utilize the normalized excess variance ($\sigma_{\mathrm{rms}}^{2}$) and probe variability on rest-frame timescales of several months and years by calculating $\sigma_{\mathrm{rms}}^{2}$ from different parts of our light curves. In addition, we derive the rest-frame optical PSD for our sources using continuous-time autoregressive moving average (CARMA) models. We observe that the excess variance and the PSD amplitude are strongly anti-correlated with wavelength, bolometric luminosity and Eddington ratio. There is no evidence for a dependency of the variability amplitude on black hole mass and redshift. These results suggest that the accretion rate is the fundamental physical quantity determining the rest-frame UV/optical variability amplitude of quasars on timescales of months and years. The optical PSD of all of our sources is consistent with a broken power law showing a characteristic bend at rest-frame timescales ranging between $\sim$100 and $\sim$300 days. The break timescale exhibits no significant correlation with any of the fundamental AGN parameters. The low frequency slope of the PSD is consistent with a value of $-1$ for most of our objects, whereas the high frequency slope is characterized by a broad distribution of values between $\sim-2$ and $\sim-4$. These findings unveil significant deviations from the simple "damped random walk" model, frequently used in previous optical variability studies. We find a weak tendency for AGNs with higher black hole mass having steeper high frequency PSD slopes., Comment: Accepted by A&A, 23 pages, 19 figures

Published
2015

33. Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-ray Blazar PG 1553+113

Author

Lat, The Fermi Collaboration, Ackermann, M., Ajello, M., Albert, A., Atwood, W. B., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Becerra Gonzalez, J., Bellazzini, R., Bissaldi, E., Blandford, R. D., Bloom, E. D., Bonino, R., Bottacini, E., Bregeon, J., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caputo, R., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Cecchi, C., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Cohen-Tanugi, J., Conrad, J., Cutini, S., D Ammando, F., Angelis, A., Palma, F., Desiante, R., Di Venere, L., Dominguez, A., Drell, P. S., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Focke, W. B., Fuhrmann, L., Fukazawa, Y., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Godfrey, G., Green, D., Grenier, I. A., Grove, J. E., Guiriec, S., Harding, A. K., Hays, E., Hewitt, J. W., Hill, A. B., Horan, D., Jogler, T., Johannesson, G., Johnson, A. S., Kamae, T., Kuss, M., Larsson, S., Latronico, L., Li, J., Li, L., Longo, F., Loparco, F., Lott, B., Lovellette, M. N., Lubrano, P., Magill, J., Maldera, S., Manfreda, A., Max-Moerbeck, W., Mayer, M., Mazziotta, M. N., Mcenery, J. E., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nuss, E., Ohno, M., Ohsugi, T., Ojha, R., Omodei, N., Orlando, E., Ormes, J. F., Paneque, D., Pearson, T. J., Perkins, J. S., Perri, M., Pesce-Rollins, M., Petrosian, V., Piron, F., Pivato, G., Porter, T. A., Raino, S., Rando, R., Razzano, M., Readhead, A., Reimer, A., Reimer, O., Schulz, A., Sgro, C., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Suson, D. J., Takahashi, H., Thayer, J. B., Thompson, D. J., Tibaldo, L., Torres, D. F., Tosti, G., Troja, E., Uchiyama, Y., Vianello, G., Wood, K. S., Wood, M., Zimmer, S., Berdyugin, A., Corbet, R. H. D., Hovatta, T., Lindfors, E., Nilsson, K., Reinthal, R., Sillanpaa, A., Antonio Stamerra, Takalo, L. O., Valtonen, M. J., Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Univers et Particules de Montpellier (LUPM), Université Montpellier 2 - Sciences et Techniques (UM2)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Leprince-Ringuet (LLR), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS), Centre d'Etudes Nucléaires de Bordeaux Gradignan (CENBG), Université Sciences et Technologies - Bordeaux 1-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Fermi-LAT, Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Université de Montpellier (UM)-Université Montpellier 2 - Sciences et Techniques (UM2)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Ackermann M, Ajello M, Albert A, Atwood WB, Baldini L, Ballet J, Barbiellini G, Bastieri D, Gonzalez JB, Bellazzini R, Bissaldi E, Blandford RD, Bloom ED, Bonino R, Bottacini E, Bregeon J, Bruel P, Buehler R, Buson S, Caliandro GA, Cameron RA, Caputo R, Caragiulo M, Caraveo PA, Cavazzuti E, Cecchi C, Chekhtman A, Chiang J, Chiaro G, Ciprini S, Cohen-Tanugi J, Conrad J, Cutini S, DAmmando F, de Angelis A, de Palma F, Desiante R, Di Venere L, Dominguez A, Drell PS, Favuzzi C, Fegan SJ, Ferrara EC, Focke WB, Fuhrmann L, Fukazawa Y, Fusco P, Gargano F, Gasparrini D, Giglietto N, Giommi P, Giordano F, Giroletti M, Godfrey G, Green D, Grenier IA, Grove JE, Guiriec S, Harding AK, Hays E, Hewitt JW, Hill AB, Horan D, Jogler T, Johannesson G, Johnson AS, Kamae T, Kuss M, Larsson S, Latronico L, Li J, Li L, Longo F, Loparco F, Lott B, Lovellette MN, Lubrano P, Magill J, Maldera S, Manfreda A, Max-Moerbeck W, Mayer M, Mazziotta MN, McEnery JE, Michelson PF, Mizuno T, Monzani ME, Morselli A, Moskalenko IV, Murgia S, Nuss E, Ohno M, Ohsugi T, Ojha R, Omodei N, Orlando E, Ormes JF, Paneque D, Pearson TJ, Perkins JS, Perri M, Pesce-Rollins M, Petrosian V, Piron F, Pivato G, Porter TA, Raino S, Rando R, Razzano M, Readhead A, Reimer A, Reimer O, Schulz A, Sgro C, Siskind EJ, Spada F, Spandre G, Spinelli P, Suson DJ, Takahashi H, Thayer JB, Thompson DJ, Tibaldo L, Torres DF, Tosti G, Troja E, Uchiyama Y, Vianello G, Wood KS, Wood M, Zimmer S, Berdyugin A, Corbet RHD, Hovatta T, Lindfors E, Nilsson K, Reinthal R, Sillanpaa A, Stamerra A, Takalo LO, Valtonen MJ, Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Montpellier 2 - Sciences et Techniques (UM2), Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3), Aalto-yliopisto, Aalto University, Ackermann, M., Ajello, M., Albert, A., Atwood, W. B., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Becerra Gonzalez, J., Bellazzini, R., Bissaldi, E., Blandford, R. D., Bloom, E. D., Bonino, R., Bottacini, E., Bregeon, J., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caputo, R., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Cecchi, C., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Cohen Tanugi, J., Conrad, J., Cutini, S., D'Ammando, F., De Angelis, A., De Palma, F., Desiante, R., Di Venere, L., Dominguez, A., Drell, P. S., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Focke, W. B., Fuhrmann, L., Fukazawa, Y., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Godfrey, G., Green, D., Grenier, I. A., Grove, J. E., Guiriec, S., Harding, A. K., Hays, E., Hewitt, J. W., Hill, A. B., Horan, D., Jogler, T., Jóhannesson, G., Johnson, A. S., Kamae, T., Kuss, M., Larsson, S., Latronico, L., Li, J., Li, L., Longo, Francesco, Loparco, F., Lott, B., Lovellette, M. N., Lubrano, P., Magill, J., Maldera, S., Manfreda, A., Max Moerbeck, W., Mayer, M., Mazziotta, M. N., Mcenery, J. E., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nuss, E., Ohno, M., Ohsugi, T., Ojha, R., Omodei, N., Orlando, E., Ormes, J. F., Paneque, D., Pearson, T. J., Perkins, J. S., Perri, M., Pesce Rollins, M., Petrosian, V., Piron, F., Pivato, G., Porter, T. A., Rainò, S., Rando, R., Razzano, M., Readhead, A., Reimer, A., Reimer, O., Schulz, A., Sgrò, C., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Suson, D. J., Takahashi, H., Thayer, J. B., Thompson, D. J., Tibaldo, L., Torres, D. F., Tosti, G., Troja, E., Uchiyama, Y., Vianello, G., Wood, K. S., Wood, M., Zimmer, S., Berdyugin, A., Corbet, R. H. D., Hovatta, T., Lindfors, E., Nilsson, K., Reinthal, R., Sillanpää, A., Stamerra, A., Takalo, L. O., Valtonen, M. J., Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), and Université Sciences et Technologies - Bordeaux 1 (UB)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)

Subjects
galaxies: jet, jets [galaxies], Astrophysics, accretion, accretion disk, Accretion, accretion disks, BL Lacertae objects: general, BL Lacertae objects: individual (PG 1553+113), galaxies: jets, gamma rays: galaxies, gamma rays: general, Astronomy and Astrophysics, Space and Planetary Science, law.invention, accretion, law, optical, gamma rays: galaxie, gamma ray: flux, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Oscillation, Gamma ray, individual (PG 1553+113) [BL Lacertae objects], oscillation, modulation, Modulation, galaxies [gamma rays], Astrophysics - High Energy Astrophysical Phenomena, BL Lac object, Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, GLAST, blazar, Telescope, galaxie [gamma rays], AGN, Blazar, accretion disk, Astrophysics::Galaxy Astrophysics, individual: PG 1553+113 [BL Lacertae objects], BL Lacertae objects: individual, general [BL Lacertae objects], monitoring, jet [galaxies], ddc:520, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], general [gamma rays], Fermi Gamma-ray Space Telescope
Abstract

We report for the first time a gamma-ray and multi-wavelength nearly-periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope (LAT) we have discovered an apparent quasi-periodicity in the gamma-ray flux (E >100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 +/-0.08 year-period gamma-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the OVRO, Tuorla, KAIT, and CSS monitoring programs and Swift UVOT. The optical cycle appearing in ~10 years of data has a similar period, while the 15 GHz oscillation is less regular than seen in the other bands. Further long-term multi-wavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity., 8 pages, 5 figures. Accepted to The Astrophysical Journal Letters. Corresponding authors: S. Ciprini (ASDC/INFN), S. Cutini (ASDC/INFN), S. Larsson (Stockholm Univ/KTH), A. Stamerra (INAF/SNS), D. J. Thompson (NASA GSFC)

Published
2015

34. Gamma-ray activity of Seyfert galaxies and constraints on hot accretion flows

Author

Micha Szanecki, Fu-Guo Xie, Andrzej Niedźwiecki, Rafal Wojaczynski, Wojaczynski, RAFAL PAWEL, Niedźwiecki, Andrzej, Xie, Fu Guo, and Szanecki, Micha

Subjects
Accretion, Seyfert [Galaxies], Galaxies: Seyfert, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Field strength, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Black hole physic, Accretion, accretion disk, Accretion disc, Astrophysics::Solar and Stellar Astrophysics, Accretion, accretion disks, Black hole physics, Gamma rays: galaxies, Astronomy and Astrophysics, Space and Planetary Science, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), galaxie [Gamma rays], accretion disks, Gamma ray, Astronomy and Astrophysic, Galaxy, Accretion (astrophysics), Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Fermi Gamma-ray Space Telescope
Abstract

We check how the Fermi/LAT data constrain physics of hot accretion flows, most likely present in low-luminosity AGNs. Using a precise model of emission from hot flows, we examine the dependence of their gamma-ray emission, resulting from proton-proton interactions, on accretion rate, black hole spin, magnetic field strength, electron heating efficiency and particle distribution. Then, we compare the hadronic gamma-ray luminosities predicted by the model for several nearby Seyfert 1 galaxies with the results of our analysis of 6.4 years of the Fermi/LAT observations of these AGNs. In agreement with previous studies, we find a significant gamma-ray detection in NGC 6814 and we could only derive upper limits for the remaining objects, although we note marginally significant (~3 sigma) signals at the positions of NGC 4151 and NGC 4258. The derived upper limits for the flux above 1 GeV allow us to constrain the proton acceleration efficiency in flows with heating of electrons dominated by Coulomb interactions, which case is favored by X-ray spectral properties. In such flows, at most ~10% of the accretion power can be used for a relativistic acceleration of protons. Upper limits for the flux below 1 GeV can constrain the magnetic field strength and black hole spin value, we find such constraints for NGC 7213 and NGC 4151. We also note that the spectral component above ~4 GeV found in the Fermi/LAT data of Centaurus A by Sahakyan et al. may be due to hadronic emission from a flow within the above constraint. We rule out such an origin of the gamma-ray emission from NGC 6814. Finally, we note that the three Seyfert 2/starburst galaxies, NGC 4595, NGC 1068 and Circinus, show an interesting correlation of their gamma-ray luminosities with properties of their active nuclei, and we discuss it in the context of the hot flow model., Comment: A&A, in press

Published
2015
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35. Chandra observation of the Big Dipper X 1624–490

Author

N. R. Robba, R. Iaria, G. Lavagetto, T. Di Salvo, Antonino D'Ai, IARIA R, LAVAGETTO G, D'AI' A, DI SALVO T, and ROBBA N R

Subjects
Physics, stars : individual : X 1624-490, Absorption spectroscopy, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Radius, Astrophysics, accretion, accretion disk, stars : neutron, Bulk motion, Spectral line, Ion, Accretion disc, Space and Planetary Science, X-rays : star, X-rays : binarie, individual : X 1624-490, X-rays : stars, X-rays : binaries, X-rays : general [accretion, accretion disks, stars], X-rays : general, Line (formation)
Abstract

We present the results of a 73 ks long Chandra observation of the dipping source X 1624-490. During the observation a complex dip lasting 4 hours is observed. We analyse the persistent emission detecting, for the first time in the 1st-order spectra of X 1624-490, an absorption line associated to \ion{Ca}{xx}. We confirm the presence of the \ion{Fe}{xxv} K$_\alpha$ and \ion{Fe}{xxvi} K$_\alpha$ absorption lines with a larger accuracy with respect to a previous XMM observation. Assuming that the line widths are due to a bulk motion or a turbulence associated to the coronal activity, we estimate that the lines have been produced in a photoionized absorber between the coronal radius and the outer edge of the accretion disk., Comment: 8 pages, 5 figures, accepted by A&A on 13/11/2006. Revised version with minor points corrected and reference added to the used data taken from the Chandra Public Archive (Obsid 4559)

Published
2006

36. Accretion disk coronae of intermediate polar cataclysmic variables

Author

Enrico Barbera, Giovanni Peres, Salvatore Orlando, ITA, Barbera, E., Orlando, S., and Peres, G.

Subjects
Magnetohydrodynamics (MHD), Stars: flare, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Magnetosphere, Astrophysics, 01 natural sciences, law.invention, Accretion, accretion disk, Settore FIS/05 - Astronomia E Astrofisica, Intermediate polar, law, 0103 physical sciences, Radiative transfer, Astrophysics::Solar and Stellar Astrophysics, Stars: coronae, X-rays: star, 0101 mathematics, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Novae, cataclysmic variable, White dwarf, Astronomy and Astrophysics, Astronomy and Astrophysic, Thermal conduction, Accretion (astrophysics), 010101 applied mathematics, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics::Earth and Planetary Astrophysics, Magnetohydrodynamics, Astrophysics - High Energy Astrophysical Phenomena, Flare
Abstract

Context. Intermediate polar cataclysmic variables (IPCV) contain a magnetic, rotating white dwarf surrounded by a magnetically truncated accretion disk. To explain their strong flickering X-ray emission, accretion has been successfully taken into account. Nevertheless, observations suggest that accretion phenomena might not be the only process behind it. An intense flaring activity occurring on the surface of the disk may generate a corona, contribute to the thermal X-ray emission, and influence the system stability. Aims. Our purposes are: investigating the formation of an extended corona above the accretion disk, due to an intense flaring activity occurring on the disk surface; studying the effects of flares on the disk and stellar magnetosphere; assessing its contribution to the observed thermal X-ray flux. Methods. We have developed a 3D magnetohydrodynamic (MHD) model of a IPCV system. The model takes into account gravity, disk viscosity, thermal conduction, radiative losses, and coronal flare heating through heat injection at randomly chosen locations on the disk surface. To perform a parameter space exploration, several system conditions have been considered, with different magnetic field intensity and disk density values. From the results of the evolution of the model, we have synthesized the thermal X-ray emission. Results. The simulations show the formation of an extended corona, linking disk and star. The flaring activity is capable of strongly influencing the disk configuration and possibly its stability, effectively deforming the magnetic field lines. Hot plasma evaporation phenomena occur in the layer immediately above the disk. The flaring activity gives rise to a thermal X-ray emission in both the [0.1-2.0] keV and the [2.0-10] keV X-ray bands. Conclusions. An intense coronal activity occurring on the disk surface of an IPCV can affect the structure of the disk depending noticeably on the density of the disk and the magnetic field of the central object. Moreover, the synthesis of the thermal X-ray fluxes shows that this flaring activity may contribute to the observed flickering thermal X-ray emission.

Published
2017

37. Super-critical growth of massive black holes from stellar-mass seeds

Author

Massimo Dotti, Francesco Haardt, Piero Madau, Madau, P, Haardt, F, and Dotti, M

Subjects
Angular momentum, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Stellar mass, media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, black hole physics, FOS: Physical sciences, Astrophysics, accretion, accretion disk, Cosmology, General Relativity and Quantum Cosmology, accretion, galaxies: high-redshift, Radiative transfer, Astrophysics::Galaxy Astrophysics, media_common, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), accretion disks, Astronomy and Astrophysics, black hole physic, Accretion (astrophysics), Galaxy, Universe, accretion, accretion disks, cosmology: miscellaneous, Space and Planetary Science, Thin disk, cosmology: miscellaneou, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

We consider super-critical accretion with angular momentum onto stellar-mass black holes as a possible mechanism for growing billion-solar-mass holes from light seeds at early times. We use the radiatively-inefficient "slim disk" solution -- advective, optically thick flows that generalize the standard geometrically thin disk model -- to show how mildly super-Eddington intermittent accretion may significantly ease the problem of assembling the first massive black holes when the Universe was less than 0.8 Gyr old. Because of the low radiative efficiencies of slim disks around non-rotating as well as rapidly rotating holes, the mass e-folding timescale in this regime is nearly independent of the spin parameter. The conditions that may lead to super-critical growth in the early Universe are briefly discussed., Comment: 5 pages, 2 figures, matches version accepted by The Astrophysical Journal Letters

Published
2014

38. Mapping accretion and its variability in the young open cluster NGC 2264: A study based on u-band photometry

Author

Ettore Flaccomio, Giuseppina Micela, John R. Stauffer, Ann Marie Cody, Jonathan Irwin, A. P. Sousa, Lawrence Venuti, Giovanni Peres, Jean-Charles Cuillandre, Silvia H. P. Alencar, J. Bouvier, Paula S. Teixeira, Venuti, L., Bouvier, J., Flaccomio, E., Alencar, S., Irwin, J., Stauffer, J., Cody, A., Teixeira, P., Sousa, A., Micela, G., Cuillandre, J., and Peres, G.

Subjects
Stellar mass, Astrophysics::High Energy Astrophysical Phenomena, Stars: formation, Population, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Photometry (optics), Accretion rate, Accretion, accretion disk, Stars: low-ma, Astrophysics::Solar and Stellar Astrophysics, education, Astrophysics::Galaxy Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Physics, education.field_of_study, Detection threshold, Astronomy and Astrophysics, Astronomy and Astrophysic, Ultraviolet: star, Accretion (astrophysics), T Tauri star, Astrophysics - Solar and Stellar Astrophysics, individual: NGC 2264, Stars: low-mass, Stars: pre-main sequence, Ultraviolet: stars, Space and Planetary Science [Accretion, accretion disks, Open clusters and associations], Space and Planetary Science, Open clusters and associations: individual: NGC 2264, Astrophysics::Earth and Planetary Astrophysics, Open cluster
Abstract

We aim at characterizing the accretion properties of several hundred members of the star-forming cluster NGC 2264 (3 Myr). We performed a deep u,g,r,i mapping and a simultaneous u+r monitoring of the region with CFHT/MegaCam in order to directly probe the accretion process from UV excess measurements. Photometric properties and stellar parameters are determined homogeneously for about 750 monitored young objects, spanning the mass range 0.1-2 Mo. About 40% are classical (accreting) T Tauri stars, based on various diagnostics (H_alpha, UV and IR excesses). The remaining non-accreting members define the (photospheric+chromospheric) reference UV emission level over which flux excess is detected and measured. We revise the membership status of cluster members based on UV accretion signatures and report a new population of 50 CTTS candidates. A large range of UV excess is measured for the CTTS population, varying from a few 0.1 to 3 mag. We convert these values to accretion luminosities and obtain mass accretion rates ranging from 1e-10 to 1e-7 Mo/yr. Taking into account a mass-dependent detection threshold for weakly accreting objects, we find a >6sigma correlation between mass accretion rate and stellar mass. A power-law fit, properly accounting for upper limits, yields M_acc $\propto$ M^{1.4+/-0.3}. At any given stellar mass, we find a large spread of accretion rates, extending over about 2 orders of magnitude. The monitoring of the UV excess on a timescale of a couple of weeks indicates that its variability typically amounts to 0.5 dex, much smaller than the observed spread. We suggest that a non-negligible age spread across the cluster may effectively contribute to the observed spread in accretion rates at a given mass. In addition, different accretion mechanisms (like, e.g., short-lived accretion bursts vs. more stable funnel-flow accretion) may be associated to different M_acc regimes., 24 pages, 21 figures, accepted for publication in Astronomy & Astrophysics

Published
2014

39. Linking the spin evolution of massive black holes to galaxy kinematics

Author

Alberto Sesana, Enrico Barausse, Elena M. Rossi, Massimo Dotti, Institut d'Astrophysique de Paris (IAP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris 6 (UPMC), Sesana, A, Barausse, E, Dotti, M, and Rossi, E

Subjects
Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, black hole physics, galaxies: active, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, General Relativity and Quantum Cosmology (gr-qc), accretion, accretion disk, General Relativity and Quantum Cosmology, accretion, Stellar evolution, galaxies: kinematics and dynamics, Astrophysics::Galaxy Astrophysics, Physics, Star formation, accretion disks, Isotropy, quasars: supermassive black holes, Velocity dispersion, Astronomy and Astrophysics, Quasar, black hole physic, Redshift, Galaxy, Stars, Space and Planetary Science, [SDU]Sciences of the Universe [physics], galaxies: kinematics and dynamic, accretion, accretion disks, galaxies: evolution, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

We present the results of a semianalytical model that evolves the masses and spins of massive black holes together with the properties of their host galaxies along the cosmic history. As a consistency check, our model broadly reproduces a number of observations, e.g. the cosmic star formation history, the black hole mass and luminosity function and the galaxy mass function at low redshift, the black hole to bulge mass relation, and the morphological distribution at low redshift. For the first time in a semianalytical investigation, we relax the simplifying assumptions of perfect coherency or perfect isotropy of the gas fueling the black holes. The dynamics of gas is instead linked to the morphological properties of the host galaxies, resulting in different spin distributions for black holes hosted in different galaxy types. We compare our results with the observed sample of spin measurements obtained through broad K$\alpha$ iron line fitting. The observational data disfavor both accretion along a fixed direction and isotropic fueling. Conversely, when the properties of the accretion flow are anchored to the kinematics of the host galaxy, we obtain a good match between theoretical expectations and observations. A mixture of coherent accretion and phases of activity in which the gas dynamics is similar to that of the stars in bulges (i.e., with a significant velocity dispersion superimposed to a net rotation) best describes the data, adding further evidence in support to the coevolution of massive black holes and their hosts., Comment: 26 pages, 18 figures, 6 tables. Replaced to match the final version accepted for publication in The Astrophysical Journal, after major revisions following the referee's suggestions

Published
2014
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40. A relativistically broadened iron line from an Accreting Millisecond Pulsar

Author

A. Papitto, T. Di Salvo, A. D’Aì, R. Iaria, L. Burderi, A. Riggio, M. T. Menna, A. Comastri, L. Angelini, M. Cappi, Papitto, A., Di Salvo, T., D'Aì, A., Iaria, R., Burderi, L., Riggio, A., and Menna, M.

Subjects
Physics, relativity, Astrophysics::High Energy Astrophysical Phenomena, X-ray binary, Astronomy, Astrophysics::Cosmology and Extragalactic Astrophysics, Radius, Astrophysics, stars: pulsars: individual: SAX J1808.4-3658, accretion, accretion disk, profiles, X-rays: binaries, Physics and Astronomy (all) [accretion, accretion disks, line], X-rays: binarie, Neutron star, Physics and Astronomy (all), Pulsar, line: profile, Millisecond pulsar, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Emission spectrum, Astrophysics::Galaxy Astrophysics, Line (formation), Doppler broadening
Abstract

The capabilities of XMM-Newton have been fully exploited to detect a broadened iron Kα emission line from the 2.5 ms Accreting Millisecond Pulsar, SAX J1808.4-3658. The energy of the transition is compatible with fluorescence from neutral/lowly ionized iron. The observed large width (FWHM more than 1 keV) can be explained through Doppler and relativistic broadening from the inner rings of an accretion disc close to the NS. From a fit of the line shape with a diskline model we obtain an estimate of the inner disc radius of 18.0-5.6+7.6km for a 1.4 M⊙ neutron star. The disc is therefore truncated inside the corotation radius (31 km for SAX J1808.4-3658), in agreement with the observation of coherent pulsations. From our estimate of the inner disc radius, we infer that the magnetic field of the neutron star is in the range 1-5×108G. © 2010 American Institute of Physics.

Published
2010

41. Testing the theory of grain growth and fragmentation by millimeter observations of protoplanetary disks

Author

Cornelis P. Dullemond, Thomas Henning, Luca Ricci, Carsten Dominik, A. Natta, Leonardo Testi, Andras Zsom, Chris W. Ormel, Francesco Trotta, Til Birnstiel, Low Energy Astrophysics (API, FNWI), Birnstiel, T., Ricci, L., Trotta, Francesco, Dullemond, C. P., Natta, A., Testi, L., Dominik, C., Henning, T., Ormel, C. W., and Zsom, A.

Subjects
protoplanetary disk, Astronomy, FOS: Physical sciences, stars: pre-main-sequence, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, accretion, accretion disk, circumstellar matter, Spectral slope, planets and satellites: formation, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Galaxy Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Physics, Earth and Planetary Astrophysics (astro-ph.EP), Physical model, Research Programm of Institute for Mathematics, Astrophysics and Particle Physics, Astronomy and Astrophysics, Astronomy and Astrophysic, Grain size, Grain growth, Stars, Wavelength, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Ophiuchus, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Millimeter, Astrophysics::Earth and Planetary Astrophysics, submillimeter: star, Astrophysics - Earth and Planetary Astrophysics
Abstract

Context. Observations at sub-millimeter and mm wavelengths will in the near future be able to resolve the radial dependence of the mm spectral slope in circumstellar disks with a resolution of around a few AU at the distance of the closest star-forming regions. Aims. We aim to constrain physical models of grain growth and fragmentation by a large sample of (sub-)mm observations of disks around pre-main sequence stars in the Taurus-Auriga and Ophiuchus star-forming regions. Methods. State-of-the-art coagulation/fragmentation and disk-structure codes are coupled to produce steady-state grain size distributions and to predict the spectral slopes at (sub-)mm wavelengths. Results. This work presents the first calculations predicting the mm spectral slope based on a physical model of grain growth. Our models can quite naturally reproduce the observed mm-slopes, but a simultaneous match to the observed range of flux levels can only be reached by a reduction of the dust mass by a factor of a few up to about 30 while keeping the gas mass of the disk the same. This dust reduction can either be due to radial drift at a reduced rate or during an earlier evolutionary time (otherwise the predicted fluxes would become too low) or due to efficient conversion of dust into larger, unseen bodies., Comment: Accepted for publication in A&A Letters. 5 pages, 3 figures

Published
2010

42. A Spectral Insight into the Physics of Accreting ms Pulsars

Author

Papitto, A, Riggio, A, Burderi, L, Menna, MT, Bozzo, E., DI SALVO, Tiziana, D'AI', Antonino, IARIA, Rosario, Papitto, A, Riggio, A, Burderi, L, Di Salvo, T, D'Ai, A, Iaria, R, Menna, MT, and Bozzo, E

Subjects
X-rays: binaries, Settore FIS/05 - Astronomia E Astrofisica, line: profile, profiles, X-rays: binaries [accretion, accretion disks, line], accretion, accretion disk
Abstract

The broadened iron lines observed from accreting compact objects are most easily interpreted in terms of reflection onto the accretion disc of the hard X-ray photons emitted by the central source. In this context, such a broadness is due to the relativistic motion of the reflecting plasma, in the deep gravitational well of the compact object, and can thus serve as a probe of the inner radius of the disc. Here we report about the discovery of such features from a couple of accreting millisecond pulsars, and discuss the constraints which can be derived on the magnetospheric radius.

Published
2010

43. Timing an Accreting Millisecond Pulsar: Measuring the Accretion Torque in IGR J00291+5934

Author

R. Iaria, N. R. Robba, T. Di Salvo, M. T. Menna, Luigi Stella, F. D'Antona, Luciano Burderi, G. Lavagetto, Alessandro Papitto, Alessandro Riggio, BURDERI, L, DI SALVO, T, LAVAGETTO, G, MENNA, MT, PAPITTO, A, RIGGIO, A, IARIA, R, D'ANTONA, F, ROBBA, N, STELLA, L, BURDERI L, DI SALVO T, RIGGIO A, MENNA M T, LAVAGETTO G, PAPITTO A, IARIA R, ROBBA N R, and STELLA L

Subjects
neutron, stars : magnetic fields, pulsars : general, pulsars : individual : IGR J00291+5934, X-ray : binaries [accretion, accretion disks, stars], X-rays : binaries, Astrophysics::High Energy Astrophysical Phenomena, X-ray binary, FOS: Physical sciences, Astrophysics, accretion, accretion disk, X-ray : binaries, Binary pulsar, Luminosity, symbols.namesake, Pulsar, Millisecond pulsar, Astrophysics::Solar and Stellar Astrophysics, pulsars : individual (IGR J00291+5934), Physics, Accretion (meteorology), general, stars : neutron, X-rays : binaries [pulsars], Astrophysics (astro-ph), Static timing analysis, Astronomy, stars : magnetic field, Astronomy and Astrophysics, Neutron star, Space and Planetary Science, symbols, Astrophysics::Earth and Planetary Astrophysics, Doppler effect, X-ray pulsar
Abstract

We performed a timing analysis of the fastest accreting millisecond pulsar IGR J00291+5934 using RXTE data taken during the outburst of December 2004. We corrected the arrival times of all the events for the orbital (Doppler) effects and performed a timing analysis of the resulting phase delays. In this way we have the possibility to study, for the first time in this class of sources, the spin-up of a millisecond pulsar as a consequence of accretion torques during the X-ray outburst. The accretion torque gives us for the first time an independent estimate of the mass accretion rate onto the neutron star, which can be compared with the observed X-ray luminosity. We also report a revised value of the spin period of the pulsar., 7 pages including 1 figure. Accepted for publication by ApJ; revised version including proof corrections

Published
2007

44. The broad-band spectrum of Cyg X-2 with INTEGRAL

Author

Luigi Stella, R. Iaria, T. Di Salvo, Mariano Mendez, Maurizio Falanga, Luciano Burderi, N. R. Robba, Walter H. G. Lewin, M. van der Klis, G. Lavagetto, High Energy Astrophys. & Astropart. Phys (API, FNWI), LAVAGETTO G, DI SALVO T, FALANGA M, IARIA R, ROBBA N R, BURDERI L, LEWIN W H G, MENDEZ M, STELLA L, and VAN DER KLIS M

Subjects
Physics, stars : individual : Cygnus X-2, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Spectrum (functional analysis), FOS: Physical sciences, Broad band, Astronomy and Astrophysics, Radius, Astrophysics, accretion, accretion disk, stars : neutron, Spherical geometry, Space and Planetary Science, binaries : close, Optical depth (astrophysics), Electron temperature, close, stars : neutron [accretion, accretion disks, binaries]
Abstract

We study the broad band (3-100 keV) spectrum of Cygnus X-2 with INTEGRAL. We find that the spectrum is well fitted by a Comptonized component with a seed-photons temperature of ~1 keV, an electron temperature of ~3 keV and an optical depth tau ~ 8. Assuming spherical geometry, the radius of the seed-photons emitting region is ~17 km. The source shows no hard X-ray emission; it was detected only at a 3 sigma level above 40 keV. We also analyzed public ISGRI data of Cyg X--2 to investigate the presence of a hard X-ray component. We report the possible presence of hard X-ray emission in one data set., Comment: 4 pages, 2 figures; Accepted for publication as a Research Note on A&A

Published
2006

45. Chandra Observation of the Dipping Source XB 1254-690

Author

T. Di Salvo, A. D' Ai', G. Lavagetto, N. R. Robba, R. Iaria, IARIA R, DI SALVO T, LAVAGETTO G, D'AI' A, and ROBBA N R

Subjects
Physics, Absorption spectroscopy, Turbulence, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Radius, EPIC, accretion, accretion disk, Bulk motion, Line width, stars : individual : XB 1254-690, stars : neutron, Ion, line : identification, Accretion disc, Space and Planetary Science, X-rays : star, individual : XB 1254-690, X-rays : stars, X-rays : binaries, line : identification [accretion, accretion disks, stars], X-rays : binarie
Abstract

We present the results of a 53 ks long Chandra observation of the dipping source XB 1254--690. During the observation neither bursts or dips were observed. From the zero-order image we estimated the precise X-ray coordinates of the source with a 90% uncertainty of 0.6\arcsec. Since the lightcurve did not show any significant variability, we extracted the spectrum corresponding to the whole observation. We confirmed the presence of the \ion{Fe}{xxvi} K$_\alpha$ absorption lines with a larger accuracy with respect to the previous XMM EPIC pn observation. Assuming that the line width were due to a bulk motion or a turbulence associated to the coronal activity, we estimate that the lines were produced in a photoionized absorber between the coronal radius and the outer edge of the accretion disk., Comment: 8 pages, 10 figs, accepted by A&A on 6 December 2006

Published
2006
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46. Variability of ultraluminous X-ray sources in the Cartwheel Ring

Author

Wolter, A, Trinchieri, G, COLPI, MONICA, Wolter, A, Trinchieri, G, and Colpi, M

Subjects
Black hole physic, Accretion, accretion disk, Physics and Astronomy (miscellaneous), Galaxies: individual (Cartwheel), Aerospace Engineering, Galaxies: stellar content, X-rays: binarie, X-rays: galaxie
Abstract

The Cartwheel is one of the most outstanding examples of a dynamically perturbed galaxy where star formation is occurring inside the ringlike structure. In previous studies with Chandra, we detected 16 Ultra Luminous X-ray sources lying along the southern portion of the ring. Their Luminosity Function is consistent with them being in the high luminosity tail of the High Mass X-ray Binaries distribution, but with one exception: source N.10. This source, detected with Chandra at LX = 1 1041 erg s1, is among the brightest nonnuclear sources ever seen in external galaxies. Recently, we have observed the Cartwheel with XMM-Newton in two epochs, six months apart. After having been at its brightest for at least 4 years, the source has dimmed by at least a factor of two between the two observations. This fact implies that the source is compact in nature. Given its extreme isotropic luminosity, there is the possibility that the source hosts an accreting intermediatemass black hole. Other sources in the ring vary in flux between the different datasets. We discuss our findings in the context of ULX models. © 2007 International Astronomical Union.

Published
2006

47. The iron K-shell features of MXB 1728-34 from a simultaneous Chandra-RXTE observation

Author

T. Di Salvo, Mariano Mendez, R. Iaria, Antonino D'Ai, G. Lavagetto, N. R. Robba, Luciano Burderi, Luigi Stella, Walter H. G. Lewin, M. van der Klis, D'AI' A, DI SALVO T, IARIA R, MENDEZ M, BURDERI L, LAVAGETTO G, LEWIN W H G, ROBBA N R, STELLA L, VAN DER KLIS M, and High Energy Astrophys. & Astropart. Phys (API, FNWI)

Subjects
Physics, Astrophysics::High Energy Astrophysical Phenomena, individual : MXB 1728-34, stars : neutron, X-rays : stars, X-rays : binaries, X-rays : general [accretion, accretion disks, stars], Astrophysics (astro-ph), X-ray binary, Electron shell, Astronomy, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, accretion, accretion disk, Neutron star, Absorption edge, Space and Planetary Science, Ionization, X-rays : star, Black-body radiation, Emission spectrum, Basso continuo, X-rays : binarie, stars : individual : MXB 1728-34, X-rays : general
Abstract

We report on a simultaneous Chandra and RossiXTE observation of the low-mass X-ray binary atoll bursting source MXB 1728-34 performed on 2002 March 3-5. We fit the 1.2-35 keV continuum spectrum with a blackbody plus a Comptonized component. Large residuals at 6-10 keV can be fitted by a broad (FWHM ~ 2 keV) Gaussian emission line or, alternatively, by two absorption edges associated with lowly ionized iron and Fe XXV/XXVI at ~7.1 keV and ~9 keV, respectively. In this interpretation, we find no evidence of broad, or narrow, emission lines between 6 and 7 keV. We test our alternative modelling of the iron K shell region by reanalysing a previous BeppoSAX observation of MXB 1728-34, finding a general agreement with our new spectral model., Comment: 6 pages, 4 figures. Accepted for publication by A&A

Published
2006

48. High Resolution and Broad Band Spectra of Low Mass X-ray Binaries: A Comparison between Black Holes and Neutron Stars

Author

Luciano Burderi, N. R. Robba, R. Iaria, T. Di Salvo, DI SALVO T, IARIA R, ROBBA N, and BURDERI L

Subjects
Physics, High-energy astronomy, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), X-ray, FOS: Physical sciences, Broad band, Astronomy and Astrophysics, Astrophysics, individual : Sco X-1, 4U 1705-44, stars : neutron, X-rays : stars, X-rays : binaries, X-rays : general [accretion, accretion disks, stars], Compact star, accretion, accretion disk, Spectral line, Black hole, Neutron star, General Relativity and Quantum Cosmology, stars : individual : Sco X-1, 4U 1705-44, Space and Planetary Science, X-rays : star, X-rays : binarie, Low Mass, X-rays : general
Abstract

A common question about compact objects in high energy astrophysics is whether it is possible to distinguish black hole from neutron star systems with some other property that is not the mass of the compact object. Up to now a few characteristics have been found which are typical of neutron stars (like quasi periodic oscillations at kHz frequencies or type-I X-ray bursts), but in many respects black hole and neutron star systems show very similar behaviors. We present here a spectral study of low mass X-ray binaries containing neutron stars and show that these systems have spectral characteristics that are very similar to what is found for black hole systems. This implies that it is unlikely we can distinguish between black holes and neutron stars from their X-ray spectra, except for the fact that black hole systems show sometimes a more extreme behavior with respect to neutron star systems., Proceedings of the Frascati Workshop 2005: Multifrequency Behaviour of High Energy Cosmic Sources, Vulcano, May 23-28. 13 pages including 4 figures

Published
2005

49. A Broad Iron Line in the Chandra High Energy Transmission Grating Spectrum of 4U 1705-44

Author

Luciano Burderi, R. Iaria, G. Lavagetto, Mariano Mendez, N. R. Robba, Luigi Stella, M. van der Klis, T. Di Salvo, DI SALVO, T, IARIA, R, MENDEZ, M, BURDERI, L, LAVAGETTO, G, ROBBA, N, STELLA, L, VAN DER KLIS, M, and High Energy Astrophys. & Astropart. Phys (API, FNWI)

Subjects
Physics, Spectrometer, Astrophysics::High Energy Astrophysical Phenomena, X-rays : stars, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, accretion, accretion disk, stars : individual (4U 1705-44), Corona, stars : neutron, Neutron star, Full width at half maximum, Space and Planetary Science, individual (4U 1705-44), X-rays : binaries, X-rays : general, X-rays : stars [accretion, accretion disks, stars], Reflection (physics), Emission spectrum, Low Mass, X-rays : binarie, Line (formation)
Abstract

We present the results of a Chandra 30 ks observation of the low-mass X-ray binary and atoll source 4U 1705-44. Here we concentrate on the study of discrete features in the energy spectrum at energies below ~3 keV, as well as on the iron Kalpha line, using the High Energy Transmission Grating Spectrometer on board the Chandra satellite. Below 3 keV, three narrow emission lines are found at 1.47, 2.0, and 2.6 keV. The 1.47 and 2.6 keV lines are probably identified with Lyalpha emission from Mg XII and S XVI, respectively. The identification of the feature at ~2.0 keV is uncertain because of the presence of an instrumental feature at the same energy. The iron Kalpha line at ~6.5 keV is found to be intrinsically broad (FWHM~1.2 keV); its width can be explained by reflection from a cold accretion disk extending down to ~15 km from the neutron star center or by Compton broadening in the external parts of a hot (~2 keV) Comptonizing corona. We finally report here precise X-ray coordinates of the source.

Published
2005

50. On the soft excess in the x-ray spectrum of circinus X-1: Revisitation of the distance to circinus X-1

Author

Luciano Burderi, R. Iaria, F. Frontera, T. Di Salvo, M. van der Klis, R. P. Fender, N. R. Robba, M. Spanò, Iaria, R., Spano, M., DI Salvo, T., Robba, N., Burderi, L., Fender, R., Van Der Klis, M., Frontera, F., and High Energy Astrophys. & Astropart. Phys (API, FNWI)

Subjects
Physics, Electron density, Accretion, Absorption spectroscopy, Stars: Individual: Constellation Name: Circinus X-1, Stars: individual (Circinus X-1), Accretion Disks, Stars: Neutron, X-Rays: Binaries, X-Rays: Stars, X-ray, Astronomy and Astrophysics, individual (Circinus X-1), Stars: neutron, X-rays: binaries, X-rays: stars, Nuclear and High Energy Physics, Space and Planetary Science [Accretion, accretion disks, Stars], Astrophysics, Compact star, X-rays: binarie, Spectral line, Accretion, accretion disk, Space and Planetary Science, Ionization, Circinus, X-rays: star, Absorption (logic), Nuclear and High Energy Physic
Abstract

We report on a 300 ks BeppoSAX (0.12-200 keV) observation of Circinus X-1 (Cir X-1) at phases between 0.62 and 0.84 and on a 90 ks BeppoSAX observation of Cir X-1 at phases 0.11-0.16. Using the canonical model adopted until now to fit the energy spectrum of this source, large residuals appear below 1 keV. These are well fitted using an equivalent hydrogen column of 0.66¿1022 cm-2, adding absorption edges of O VII, O VIII, and Ne IX in the spectra extracted from the observation at phases 0.62-0.84 and adding absorption edges of O VII, O VIII, Mg XI, and Mg XII and absorption lines of O VIII and Mg XII in the spectra extracted from the observation at phases 0.11-0.16. During the observation at phases 0.62-0.84 the electron density associated with the ionized matter is ~1013 cm-3, remaining quite constant going away from the compact object. During the observation at phases 0.11-0.16, the electron density profile varies along the distance going from ~6¿1013 cm-3 at ~1011 cm to ~9¿1010 cm-3 at ~1013 cm. The equivalent hydrogen column toward Cir X-1 is 3 times lower than the value obtained from previous models. This low value would imply that Cir X-1 is at a distance of 4.1 kpc.

Published
2005

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